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Comparing Arrays Javascript: Javascript Explained

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Comparing arrays in JavaScript is a useful method for producing meaningful data from sets of array values. The process of comparing two arrays is known as ‘array intersection’ and it enables developers to identify similarities and differences between two sets of data. This article will explore the different methods of comparing arrays available in JavaScript and look at examples of the process in use.

What is an Array in Javascript?

An array is a data structure used in JavaScript to store a set of values. JavaScript arrays can either contain strings, numbers or objects. Suppose you had a JSON array that looked like this:

  const array = [{      name: 'John',      age: 25    },    {      name: 'Sally',      age: 40  }];

In this example, we have an array containing two objects. Each object has two key-value pairs; ‘name’ and ‘age’. An array can have an unlimited number of items and each item can be of any type.

How to Compare Arrays in Javascript

Once you have two arrays, there are a few methods you can use to compare them. We will explore the ‘looping’ method and the ‘JSON’ method.

Using the Looping Method

The looping method is one of the simplest ways to compare two arrays. It involves looping through each array and seeing if the values in both arrays match. If a value is found to be present in both arrays, then it can be added to a new array that contains only the values found in both source arrays.

For example, if we had the following two arrays:

  const array1 = [1, 2, 3];  const array2 = [2, 3, 4];

We could use the following loop to compare them:

  const intersectionArray = [];  for (let value of array1) {    if (array2.includes(value)) {      intersectionArray.push(value);    }  }

In this example, we have declared an empty array called ‘intersectionArray’. We then loop through ‘array1’ and use the ‘includes’ method to check if ‘array2’ contains the same value. If it does, then we add it to our ‘intersectionArray’.

The resulting intersection array for our example would look like this:

  intersectionArray = [2, 3];

Using the JSON Method

The JSON method is slightly more complicated than the looping method. It involves converting both arrays into JSON strings, then comparing them. The process looks something like this:

  let array1 = [1, 2, 3];   let array2 = [2, 3, 4];  let string1 = JSON.stringify(array1);   let string2 = JSON.stringify(array2);  if (string1 == string2) {      // matching arrays   ×××××××××××××××××××××    } else {   /// not matching arrays    ××××××××××     // not matching arrays  ××××××××××    }  

In this example, we use the ‘JSON.stringify’ method to covert both arrays into strings. We then compare the two strings. If they are identical, then we know that the two arrays contain the same values.

Finding the Intersection of Two Arrays

The process of finding the intersection of two arrays involves finding any values that are present in both source arrays. This can be done with both the looping and JSON methods. With either method, the resulting array will contain only the elements that appear in both source arrays.

Finding the Difference Between Two Arrays

The process of finding the difference between two arrays involves finding any values that are not present in both source arrays. This can be done with both the looping and JSON methods. With either method, the resulting array will contain only the elements that appear in one source array and not the other.

Examples of Comparing Arrays in Javascript

The following example uses the looping method to compare two arrays and find any elements present in both:

  const array1 = [1, 2, 3];   const array2 = [2, 3, 4];  const intersectionArray = [];  for (let value of array1) {   // looping through first array  ×××××  ×      if (array2.includes(value)) {      // if second array includes current value   ×××× × ×        intersectionArray.push(value);        // add value to intersectionArray    × × ×    ×       }   // closes if statement   × × × ×   ×   ×   ×   ×    ■     }   // closes for loop   ×   ×   ×   ■    ×   ■    console.log(intersectionArray); // [2,3]   ■    ×   ■   ■      ◆      ◆        ◆        				◆ 			 			◆ 						     ◆ 					   		◆ 			   		                 	              	◆ 			                    ◆ 			                      ◆                        ◆                                 ◆                             ◆                           ◆                               ◆                                                              ophical poiando                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        ◆ ​◆​ ◆ ◆ ◆ ​◆ ​◆​ ◆ ◆ ◆​ ◆ ​◆​ ◆ ◆ ◆​ ◆ ​◆​ ◆ ◆ ◆​ ◆ ​◆​ ◆ ◆ ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ••• •••• •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 

Benefits of Comparing Arrays in Javascript

Comparing arrays in JavaScript has many benefits. It saves time as you don’t have to manually search through each value, and it also reduces errors as it eliminates the possibility of missing one or more values. Additionally, by using comparison methods it is possible to produce new data sets that contain only values found in both source arrays. This can be used to quickly identify similarities and differences between sets.

Common Pitfalls to Avoid

When comparing arrays, it is important to be aware of the type of data being used. If two arrays contain either objects or strings, then you must use the JSON method to do a comparison. Additionally, it’s important to check that any loops are written correctly so as not to miss any potential matches.

Anand Das

Anand Das

Anand is Co-founder and CTO of Bito. He leads technical strategy and engineering, and is our biggest user! Formerly, Anand was CTO of Eyeota, a data company acquired by Dun & Bradstreet. He is co-founder of PubMatic, where he led the building of an ad exchange system that handles over 1 Trillion bids per day.

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