Trending February 2024 # How Union Works In Linq With Examples? # Suggested March 2024 # Top 2 Popular

You are reading the article How Union Works In Linq With Examples? updated in February 2024 on the website Cancandonuts.com. We hope that the information we have shared is helpful to you. If you find the content interesting and meaningful, please share it with your friends and continue to follow and support us for the latest updates. Suggested March 2024 How Union Works In Linq With Examples?

Introduction to LINQ Union

Web development, programming languages, Software testing & others

Syntax:

Let’s see the LINQ Union method syntax as follows,

If you are working with complex types of union collection, then you must make use of the IEqualityComparer interface to get an accurate result; otherwise, you will get only the incorrect result.

How does Union work in LINQ?

In LINQ Union method it only supports the method syntax; the query syntax will not be available in the union method. The Queryable and Enumerable classes will be acceptable in the union method. The Union operator or method is mainly used to combine the multiple collections into a single distinct collection; it returns only the unique elements; as a result, it removes the duplicate values from the collection. Let’s see one example as follows.

For Example,

Collection X= {20, 40, 60, 80, 100} Collection Y= {20, 40, 70} var _result = X.Union(Y);

The result is = {20, 40, 60, 70, 80, 100} in this resultant collection, the elements 20 and 40 appear in both the collection, so in the result, it returns only once because unique elements are only displayed it eliminates the duplications. Let’s see the working flow of the unique method as follows,

static public void Main() { string[] Department1 = { "JAVA", "DOTNET", "PHYTHON", "ANDROID" }; string[]Department2 = { "JAVA", "ANDROID", "DESIGNING" }; var unionResult = Department1.Union(Department2); foreach (var items in unionResult) { Console.WriteLine(items); } } string[]Department1 = { "JAVA", "DOTNET", "PHYTHON", "ANDROID" }; string[]Department2 = { "JAVA", "ANDROID", "DESIGNING" };

From this, we have to return only the unique elements from both the collections it removes the duplications from both collections, to get all the elements uniquely, we need to go with the Union () method,

var unionResult = Department1.Union(Department2);

It returns only the unique elements from the collection, in which it removes the repeated elements present in the collection it returns only once; let’s check the result here below,

Result is {"JAVA", "DOTNET","DESIGNING", "PHYTHON", "ANDROID"}; Usage of IEqualityComparer Interface

Here we introduce the IEqualityComparer Interface for the union method because the union method can’t be able to differentiate whether the two types are equal; it does not work with complex types of collection, so it returns the only incorrect result. For this purpose, we have to build a new comparer class to implement IEqualityComparer Interface to get an accurate result. IEqualityComparer Interface has two different methods, GetHashCode and Equals methods; we need to implement both methods compulsory. Let’s see one example for IEqualityComparer interface and lets us assume the Book Class contains BookID and BookName,

{ public bool Equals(Book x, Book y) { if (x.BookID == y.BookID && x.BookName.ToLower() == y. BookName.ToLower()) return true; return false; } public int GetHashCode(Student obj) { return obj. BookID.GetHashCode(); } }

Now can send the BookComparer class in the Union extension method to get the accurate results.

BookList _1.Add(new BookClass { BookID = 1001, BookName = “The Writer” }); BookList _1.Add(new BookClass { BookID = 1002, BookName = ” Success ” }); BookList _1.Add(new BookClass { BookID = 1003, BookName = “Life Secret ” }); BookList _2.Add(new BookClass { BookID = 1002, BookName = “Success” }); BookList _3.Add(new BookClass { BookID = 1005, BookName = “Team Lead ” }); var _resultUnion = BookList _1.Union(BookList _2, new BookComparer()); foreach (BookClass res in _resultUnion) Console.WriteLine(res. BookName);

The result will be” The Writer, Success, Life Secret, Team Lead,” it returns only the unique elements from the collection, in which it removes the repeated elements.

Example

Code:

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace Console_LINQUnion { class Linq_Union { internal class DoctorClass { public int DoctorID { get; set; } public string DoctorName { get; set; } } { public bool Equals(DoctorClass a, DoctorClass b) { if(a.DoctorID==b.DoctorID&&b.DoctorName.ToLower()==b.DoctorName.ToLower()) { return true; } return false; } public int GetHashCode(DoctorClass obj) { return obj.DoctorID.GetHashCode(); } } public class Program { public static void Main(string[] args) { DoctorList_1.Add(new DoctorClass { DoctorID = 1001, DoctorName = "Smith" }); DoctorList_1.Add(new DoctorClass { DoctorID = 1002, DoctorName = "Rio" }); DoctorList_1.Add(new DoctorClass { DoctorID = 1003, DoctorName = "Dev" }); DoctorList_1.Add(new DoctorClass { DoctorID = 1004, DoctorName = "Jack" }); DoctorList_1.Add(new DoctorClass { DoctorID = 1005, DoctorName = "Ricky" }); DoctorList_2.Add(new DoctorClass { DoctorID = 1002, DoctorName = "Rio" }); DoctorList_2.Add(new DoctorClass { DoctorID = 1003, DoctorName = "Dev" }); DoctorList_2.Add(new DoctorClass { DoctorID = 1007, DoctorName = "Peter" }); DoctorList_2.Add(new DoctorClass { DoctorID = 1009, DoctorName = "Raj" }); DoctorList_2.Add(new DoctorClass { DoctorID = 1001, DoctorName = "Smith" }); var _resultUnion = DoctorList_1.Union(DoctorList_2, new DoctorComparer()); Console.WriteLine("USING LINQ-UNION WITH IEqualityComparer"); Console.WriteLine("List of Unique Doctor-Namesn"); foreach (DoctorClass val in _resultUnion) Console.WriteLine(val.DoctorName); Console.ReadLine(); } } } }

Output:

Conclusion

The article LINQ Union essentially used to combine the collection of elements and returns distinct elements; as a result, when working on complex types of huge data, we need to implement the IEqualityComparer Interface. I hope the article helps out without any doubt by seeing the examples programmatically.

Recommended Articles

This is a guide to LINQ Union. Here we discuss the Introduction, syntax, How Union works in LINQ along with Examples and code implementation. You may also have a look at the following articles to learn more –

You're reading How Union Works In Linq With Examples?

How Println Works In Kotlin With Examples?

Introduction to Kotlin println

Web development, programming languages, Software testing & others

Syntax

The kotlin language uses many default keywords, variables, and functions to implement the mobile-based applications, with some pre-defined keywords, including the functions. Like that, println() is the default function for handling and print the statements, which the coder declares.

{ val variablename= values println(“coder statements and ${variablename}””) var var2= values println(“coder statements and $var2”) }

The above codes are the basic syntax for utilising the println() method and its statements used by the kotlin language. Then, based on the user scenario, we can print the outputs on the console screen.

How does println work in Kotlin?

Using the println() method, the coder prints the statements and the outputs the programmer enters, and it depends on the application point of view. The programmer entered all the codes like keywords, variables, functions, and classes that have both primary and secondary classes. Some nested classes concept implements the parent class with the child class, and then it’s called by the specific packages. For each method, both default and customized methods used the println() statements.

The println() method has similar to the print() method but some difference is there like print() method prints the string inside of the quotes and println() method print the strings inside the quotes which is similar like print() method but the mouse cursor which automatically moves to the next line of the console screen. We can use the expressions and catch the exceptions and errors instance whenever it requires like the try-catch statement is used for handling the exceptions block, but the catch and finally blocks to capture and print the exceptions using the print and println() method. And also, when we want to print the variable inside the println() method, we can use the dollar($) symbol followed by either var and val names along with inside of the double-quoted string literals.

Examples of Kotlin println

Given below are the examples of Kotlin println:

Example #1

Code:

import java.util.Scanner class examp1{ fun demo() { val strinp="Welcome To My Domain its the first example that related to the kotlin println() statement" mlist.add("Please add the first input") mlist.add("Please add the second input") mlist.add("Please add the third input") mlist.add("Please add the fourth input") mlist.add("Please add the fifth input") println("Please follow the below loop iteration") for(vlist in mlist){ println(vlist) } println("Thank you users your mutablelist datas are entered successfully") println(mlist[1]) mlist.add(1,"June") println("We can modify the first mutable list value as mlist.add(1,"June")") for(vlist in mlist){ println(vlist) } mlist.add("July") println("Again we can add one more list values mlist.add("July")") for(vlist in mlist){ println(vlist) } mlist.addAll(2,finp1) println("We can add all the list values into the single list: mlist.addAll(1,finp1)") for(vlist in mlist){ println(vlist) } mlist.addAll(finp) println("We can add all the values and make it to the single list: mlist.addAll(finp)") for(vlist in mlist){ println(vlist) } mlist.remove("July") println("We can remove the specified values: mlist.remove("July")") for(vlist in mlist){ println(vlist) } } } val num = 41.83 println("Your input num is:") println("$num") println("num = $num") println("${num + num}") println(41.83) val sc = Scanner(System.`in`) print("Please enter your input number: ") var il:Int = sc.nextInt() println("You entered input is: $il") var ob=examp1() ob.demo() }

Output:

Example #2

Code:

import java.util.Date import java.text.SimpleDateFormat class Exam2() { var id: Int = 0 var sname: String = "" var city: String = "" fun demo2(){ val sinp="41,Sivaraman, Chennai" println(sinp) } } enum class Second(var sec: String) { demo("Welcome To My Domain its the second example that related to the kotlin println()"){ override fun sample() { println("Thank you users have a nice day") } }, demo1("We can override the sample method"){ override fun sample() { println("Current month is june") } }, demo2("Again we override the sample method"){ override fun sample() { println("Next month is july") } }; abstract fun sample() fun demo1(svalues: String): String{ return "Have a Nice day users" } } val inp1 = Exam2() var sinp=inp1.demo2() println(SimpleDateFormat("yyyy-MM-ddX").parse("2024-06-22+00")) println("Welcome To My Domain its the second example that related to the kotlin println() method, $sinp") println("Hello users") println(41) println(1234567L) println(0b01001111) println(41.32) println(41.762F) println('a') println(true) println() var st = "Hello users thank you for spenting ur time with us" println(st) println(st) }

Output:

In the second example, we used the date format package utilised in the kotlin codes with some operations like integer, string, float, double and boolean datatype values printed on the output console.

Example #3 import java.util.Scanner try { val inpread = Scanner(System.`in`) println("Welcome To My Domain its the third example that related to the kotlin println()") println("Please enter your inputs") var id = inpread.nextInt() println("Your input id is "+id) demo(41,83,lamb) val inpdata = 12 / 4 println(inpdata) } catch (e: NullPointerException) { println(e) } finally { println("finally block always executed whenever try is executing") } println("Have in Nice Day users please try again") } val result = in1 + in2 println(result) }

Output:

In the final example, we used the try-catch block for handling the exceptions and performed the arithmetic operations using the lambda expressions.

Conclusion

In kotlin language, we used many default methods, classes, and keywords to implement the application. So all the programming logic will be implemented using some codes like classes and methods eventhough some additional operations are performed, results are printed on the output console by using the print() and println() methods.

Recommended Articles

This is a guide to Kotlin println. Here we discuss the introduction, syntax, and working of println in Kotlin along with different examples and code implementation. You may also have a look at the following articles to learn more –

How Function Works In Scala With Examples

Definition of Scala Function

As the name suggests, Scala Function means a piece of code supposed to do a function. Like any other programming language scala, Function works in the same way. The function is nothing but a way to writing our logic in a separate part, or we can say a function is a group of statements that are responsible for performing some specific task. The function can be used where we have the same logic or repetitive code, so instead of writing the code again and again, we can create one function and call that from everywhere. Scala function is also responsible for performing a specific task.

Start Your Free Software Development Course

Web development, programming languages, Software testing & others

How to Define Functions in Scala? defname_of_function ([parametre_list]) : [return_type] = { }

Scala Function contained 6 parts while defining; let’s discuss them one by one.

def: It is a keyword that is available in scala. If you want to define any function, we have to use this keyword at the beginning.

name_of_function: This is the user-defined name of the function. It should be similar to the logic or task that the function is going to execute while calling. Also, it should be in a camel-case (lower).

return_type: return type means what we are expecting from the function in return after executing. It can be anything, but it is optional. In java, the default return type is void, and in scale, it is Unit if we do not specify.

parametre_list: This stands for what we are providing to our function while calling. We have to specify the data type of the parameters as well while declaring inside the square brackets []. We will see them into the practice syntax below.

 =: This can be used with the return type component. It specifies, if the = is there, it means our function is going to return some value. If not, then no value we want. It is like a default return type function.

function logic: Inside this, we write the whole logic that we want to perform on the calling of function. We can also call the different functions inside this function. Remember body should be enclosed with the {} curly braces.

defcalculateSum ([a:Int, b: Int]) : Int = { return a + b; }

This way, we can define it.

How does Function work in Scala?

The function is used to perform the task. To use any function, we need to call it. Scala provides us with different ways to call a function, i.e. we can call them directly or by using the class instance.

[instance].name_of_function

or

function(list_parameter)

In scala, we have two types of functions like any other programming language.

Parameterized functions: In this type of function, we pass the list of parameters.

Non-Parameterized functions: In this type of function, we do not pass any parameters to function. That will be empty. Also, we can pass any user-defined value as a parameter also.

Let’s take one example to understand its working;

object Main extends App{ calculateSum(10, 20) defcalculateSum(a : Int, b : Int){ var result = a + b ; println("Result is  :: "+ result) } }

Above we have defined one function name calculateSum, and it is taking two variables, a and b. Both are of the Integer type. Inside the function body, we have written the logic that we want to perform. We are adding these two values, a and b, holding the value into the third variable named result. After that, we are just printing the value that we obtained. But now we have to call this function, so in the above line, we are calling the function b its name and parameter specified. The number of Parameters we passed and the number defined in the function signature should be the same; otherwise, it will give a compile-time error.

Examples of Scala Function

Examples of (simple function, parameterized function, etc.).

Example #1

This example shows the use of functions without parameters.

object Main extends App{ simpleFunction() defsimpleFunction(){ println("This is simple function") println( "without parameter. ") } }

Output:

Example #2

Code:

object Main extends App{ sum(20 , 50, 100) defsum(x: Int, y : Int, z: Int){ println("This is parameter function") var result = x + y +z println("result obtained is  :::"  +result) } }

Output:

Example #3

In this example, we are making a mixed parameter list of a function. This takes integer and string as well.

Code:

object Main extends App{ mixedFunction(20 , 50, 100, "Ajay", "Indore") defmixedFunction(x: Int, y : Int, z: Int, name: String, address: String){ println("This is parameter function") var result = x + y +z println("result obtained is  :::"  +result) println("Employee name  :: " + name) println("Employee address  :: " + address) } }

Example #4

In this example, we are taking a user-defined object and printing its value. We can take any value as a parameter.

Code:

object Main extends App{ var emp1 = new Employee("Amita", 20, 30, "Indore") employeeInfo(emp1) defemployeeInfo(emp : Employee){ println("In this we are taking one user defined parameter.") println("Passing a user value ::") } } class Employee(name: String, Id:Int, Age: Int, address: String){ }

Output:

Conclusion

Functions are used to avoid the redundant code or repetitive code. It makes our code looks simple and more understandable. Also, we can easily debug our code and identified the error, if any. These Scala functions are the same as any other programming language. Keep in mind the return type and parameter list or signature of the function while working with them.

Recommended Articles

We hope that this EDUCBA information on “Scala Function” was beneficial to you. You can view EDUCBA’s recommended articles for more information.

How Boolean Type Works In Perl With Examples

Introduction to Perl boolean

Perl boolean type is a type of value that, unlike other programming languages, behaves differently in a manner where the function using these values returns true or false. Perl programming language is not considered conventional when it comes for making the value as true or false. These values are used only for interpretation and significance that these are boolean values, not the actual values for manipulation. A boolean value is not majorly used in Perl language; rather, it is used only when the typical systems have made use of these as return types for identification and manipulation.

Start Your Free Software Development Course

Web development, programming languages, Software testing & others

Syntax:

use boolean; do &always if true_val; do &never if false_val;

The module as boolean makes use of basic as data type which is used for making the entire system comprising f values which is true or false depending on the value.

How boolean Type Works in Perl?

There are many ways to represent the boolean values in Perl for which the programmer depends or work for with the help of making the process of evaluating the conditional checking, system checking and many other factors which depends on the boolean type of Perl. These values are not any kind of special values that need to have value as true or false. On the other hand, there are a number of ways in which the value is being taken care of in terms of boolean.

There are some values that are always false in the Perl programming language, namely, ‘undef’, 0, 0.0, ‘’, ‘0’.

Boolean for Perl programming language uses other scalar values but not the naïve values like other programming languages.

Boolean in Perl can be of many types, like if in case the value comes out to be truth, then it needs conversion into the value as false depending on the type of requirement at the time of implementation.

Most often, the values come out to be false, but within that value of return, there might be some inbuild system variables which internally gets a comparison with the values and returns the value as true within it, which is mentioned in an example further.

There are times when boolean is used for undef and empty string; then, in that case, it is very much needed to make the entire set of boolean justifiable with the other values that need conversion and worthy for representation.

Using Strict and warnings for the values and the programs in execution is quite useful whenever needed to get the troubleshooting done correctly.

Strict and warning usage with the empty string in consideration sometimes provides the warning for any Perl program into execution. Also, it helps in making the overall result to be moved in some streamlined way.

There are some values as 0, which is true in some or the other way where the boolean values are text in the form of string and then when it is used, it gets converted into some type of number converted into some value with string.

There are some of the values which are considered as truth with respect to the usage of the unary operator and can be converted into a lie when used with a single operator; other than that, when double unary operator !! is used, it will be used for converting the entire value as a lie.

Examples of Perl boolean

Given below are the examples of Perl boolean:

Example #1

This program demonstrates the use of Perl statement, which is used as a conditional statement to check whether the value taken is true or false depending on the scenario and requirement.

Code:

#!/usr/bin/perl if ('even_no') { print 'true'; } else { print 'false'; }

Output:

Example #2

This program demonstrates the false values for the variable being assigned a value as 0, as shown in the output.

Code:

#!/usr/bin/perl $at_1 = 0; if ($at_1) { print "at_1 is Truen"; } else { print "at_1 is Falsen"; }

Output:

Example #3

This program demonstrates the use of undef with the condition in Perl, which is used for giving the output as shown.

Code:

#!/usr/bin/perl foreach my $vl_3 (undef, 0, 0.5, '', '8') { if ($vl_3) { print "truen"; } else { print "falsen"; } }

Example #4

This program demonstrates the empty string, which is used for checking the condition with the value to be returned as true or false as shown in the output.

Code:

#!/usr/bin/perl $bt_emp = ''; if ($bt_emp) { print "bt_emp is Truen"; } else { print "bt_emp is Falsen"; }

Output:

Example #5

This program is used for demonstrating the values by using warnings or strict as a standard file inclusion for a variable as shown in the output.

Code:

#!/usr/bin/perl use warnings; use strict; my $one_vr = undef; print $one_vr + 2;

Output:

Example #6

There are times when the value as string internally gets converted into the value as 0 and then when compared with the conditional check by evaluation is considered as shown in the output where the string is fed as an input to the value, and then it throws the value as true as shown.

Code:

#!/usr/bin/perl if ('0FR1RG') { print 'true'; } else { print 'false'; }

Output:

Example #7

This program demonstrates the use of unary operator ! which is used for making the value as truth from lie with the canonical format that is often used for manipulation.

Code:

#!/usr/bin/perl use Data::Dumper; print Dumper !!'Welcome_Everyone!';

Output:

Conclusion

Perl boolean is a type of boolean value used for making the Perl language use and identifies the return type by other methods and functions as true or false. Overall, Perl boolean, although not used so much significantly but once used, can solve many problems related to conditional check and evaluation, which programmers most often use.

Recommended Articles

This is a guide to Perl boolean. Here we discuss the introduction, how boolean type works in Perl? Along with examples, respectively. You may also have a look at the following articles to learn more –

Learn How Does Es6 Proxy Works With Examples?

Introduction to ES6 Proxy

The ES6 proxy is between the code and an object using as an ES6 proxies site, but we can use a proxy to do meta-programming activities like intercepting a call to examine or change the properties of an object with certain properties or methods called as the functions which are defined as the handler with certain properties or methods are called and functions defined in the handler offer access to the target.

Start Your Free Software Development Course

What is an ES6 proxy?

The ES6 proxy is placed between the middle of the code and an object. We can use a proxy to do meta-programming activities like intercepting a call to examine or change the properties of an object. When it comes to ES6 proxies, it has followed the certain nomenclature is used like a target. The proxy will virtualize the original object.

How to use Proxies?

The Proxies are generally meant by the specific computing terms like intermediaries between the objects with which we can communicate. Then the proxy server is meant by the device that sits between the web browser like (Chrome, Firefox, Safari, Edge, and so on) also the webserver like (Apache, Nginx, IIS, and so on) whereas the webpage is to be stored in the cookies and histories. The client requests and the response answers can be modified by using the proxy server. It can be boosted and efficient by caching frequently visited items and providing them to numerous users.

It has a number of proxy trap types like mainly get and set methods are the most useful traps. The other traps like proxy and supplement proxy handler codes. A Proxy is an object that wraps around another object (target) and intercepts the target object’s basic operations. Property search, assignment, enumeration, and function invocations are examples of basic operations.

How does ES6 Proxy work?

Generally, the ES6 module is a container for a group of JavaScript codes that can be related to one another. Especially the module’s variables and functions should be exported so that they can be accessible from the other files. However, in ES6 scripts, the modules can only be used in the strict mode. This means that the variables and functions are declared in a module that cannot be globally accessible. Mainly it focuses on the target and handler; the target is the original object that can be used for proxy wanted, and the handler is the kind of the object that can be defined the specified operations will be more intercepted and redefined the intercepted operations.

Target:

The proxy will virtualize the original object. And this could be a source JavaScript object and like the jQuery library, native objects, like arrays, or even other proxies which may be used on the servers.

Handler:

An object that can be used for to implement the proxy’s behavior. Now we’ll make a handler object that will intercept all get operations.

Traps:

Examples of ES6 Proxy

Different examples are mentioned below:

Example #1

Code:

function mthd1(x, y) { var a = Object.getOwnPropertyDescriptor( y.prototype, ‘constructor’ ); y.prototype = Object.create(x.prototype); var handler = { construct: function(target, args) { var obj = Object.create(y.prototype); this.apply(target, obj, args); return obj; }, apply: function(target, c, args) { x.apply(c, args); y.apply(c, args); } }; var prx = new Proxy(y, handler); a.value = prx; Object.defineProperty(y.prototype, ‘constructor’, a); return prx; } var v = function(n) { this.n = n; }; var w = mthd1(v, function(n, sno) { this.sno = sno; }); w.prototype.cty = ‘T’; var ins = new w(‘ins’, 32); document.getElementById(“one”).innerHTML = ins.cty; document.getElementById(“one”).innerHTML = ins.n; document.getElementById(“one”).innerHTML = ins.sno; let trg = {}; let prx = new Proxy(trg, {}); prx.tst = 3; alert(trg.tst); alert(prx.tst); for(let k in prx) alert(k);

Output:

In the above example, we used the Proxy object and the handler concept to create and handle user datas. It can be mainly classified to the object wrapping and intercept operations like reading and writing properties and other features. Basically, it handles the object them on its own; it allows for to transparently objects handled them.

Example #2

const hnd = { get: function(a, b) { return b in a ? a[b] : 45; } }; const obje = new Proxy({}, hnd); obje.x = 1; obje.y = undefined; document.getElementById(“one”).innerHTML = obje.x, obje.y; document.getElementById(“one”).innerHTML  = ‘z’ in obje, obje.z; const target = {}; const ins = new Proxy(target, {}); ins.e = 73; document.getElementById(“one”).innerHTML = target.e;

Output:

In the above example, we used the same Proxy object with all the html dom elements in the stack. The default value is whenever the property name is not in the object creation. It will be used as the get() handler method. Mainly, we are using native import JavaScript objects for which the proxy will be forwarded to all the user operations that are applied to it on the programming logic, including both UI and backend validations. And also, please note that while we use any looping conditional statements, the javascript objects work as a no-op, and it does not mean the native browser objects like DOM Elements.

New Proxy to intercept the operation

We can use a proxy for to intercept the multiple user operations mainly used as the following methods like,

get (getting property values)

apply (calling a function)

But it does not perform any single operation for calling the methods that can be intercepted. This is why method calls are split into two steps: first, we can use get to obtain a function, and then it can apply it for specific operations.

Conclusion

A proxy object which “traps” for invocations and users performed the multiple operations made to its target object. And which it can be subsequently passed through the no-operations and handled more elegantly. It can erect an impenetrable barrier around the target object, redirecting to all the operations specified mapping to the handler.

Recommended Articles

This is a guide to ES6 Proxy. Here we discuss how ES6 Proxy works and examples, and the codes and outputs. You may also have a look at the following articles to learn more –

How Count Command Works In Mongodb? (Examples)

Introduction to MongoDB count

MongoDB count is used to counting the no of a document from collections. We have found the number of documents using the count method in MongoDB. If we have used find method to show the data of collections, it will show all the data, but instead of finding if we have used count, it will display the only actual count of documents. The count is significant and useful to find the actual count of documents. It is beneficial in a large document of collections to find the no of documents only instead of displaying all the data.

Start Your Free Data Science Course

Hadoop, Data Science, Statistics & others

Syntax with parameters:

collection_name.count ()

collection_name.count (query, options)

Parameters with count query in MongoDB:

Below is the parameter description of the above syntax:

Collection name: Collection name is used to display the count of documents from the collection. Collection parameter is more important.

Count: It is used to count the no of the document from collections, we have found the number of documents using the count method.

Query: We can use a specified query to find the count of documents mentioned in the query. Using the query, we have filtered the results of documents from collections.

Limit: Limit is an optional parameter of the count method. We can return the maximum number of counts from the collection using limit.

Skip: Skip is an optional parameter of the count method. We can skip the number of matching documents before returning the result of the count of collection documents.

Hint: Hint is an optional parameter. This specifies that the index name is either string or either it is documented.

Read concern: Read concern is an optional parameter. The level is specified that the default level of real concern.

It has the following syntax:

Collation: Collation is used to the operation of count in MongoDB. Collation is an optional parameter of the count method.

How count Command works in MongoDB?

Below is the working of count method in MongoDB.

MongoDB count is used to counting the no of the document from collections.

We have found the number of documents using the count method in MongoDB.

The count is significant and useful to find the actual count of documents.

It is handy in a large document of collections to find the no of documents only instead of displaying all the data.

If we have used find method to show the data of collections, it will show all the data.

But instead of finding, if we have use count, it will display the only actual count of collection.

We can define read concern levels as local and majority. If we want to a read concern level as the majority, then we need to specify a nonempty query condition.

The default override read concern level of count method in it is local.

We can skip the count of collection documents using the skip parameter. Skip is used to skip the count of documents.

We have also used the index to return the count of the documents. For fast retrieval count of documents, we are using an index with count method.

Count method is essential and useful to display the count of all or specified documents.

Examples of MongoDB count

Given below are few of the examples:

We are taking the example of the emp_count table to describe the example of the count method in MongoDB. Below is the data description of emp_count table as follows.

Code:

db.emp_count.find ()

Output:

Example #1 – Count all documents from a collection

In the below example, we have count all documents from emp_count table using count method in MongoDB.

db.runCommand( {count: ’emp_count’ } )

Output:

The count of all the documents in emp_count table is 12. We have to find a count of documents in two ways.

Example #2 – Count documents that match a query

In the below example, we have to count the documents that match query from emp_count table using count method in MongoDB.

Code:

db.runCommand ( {count:’emp_count’, query: { emp_salary: { $gt: 10000 } } } )

Output:

In the above example, the match count of query greater than 30000 emp_salary is 4, and greater than 10000 emp_salary is 11.

Example #3 – Skip documents in the count

Code:

db.runCommand ( {count:’emp_count’, query: { emp_salary: { $gt: 10000 } }, skip: 10 } )

Output:

Example #4 – Count using default read concern

Below is the example of count using default read concern in MongoDB. We have used read concern levels as local to display the result.

Code:

db.runCommand( { count:'emp_count', query: { emp_salary: { $gt: 10000 } }, readConcern: { level: "local" } } )

Output:

Recommended Articles

This is a guide to MongoDB count. Here we discuss the Introduction, how count command works in MongoDB? Along with examples. You may also have a look at the following articles to learn more –

Update the detailed information about How Union Works In Linq With Examples? on the Cancandonuts.com website. We hope the article's content will meet your needs, and we will regularly update the information to provide you with the fastest and most accurate information. Have a great day!