How to convert CSV string file to a 2D array of objects using JavaScript ?

A CSV is a comma-separated values file with a .csv extension, which allows data to be saved in a tabular format. 

In this article, we will learn to convert the data of a CSV string to a 2D array of objects, where the first row of the string is the title row using JavaScript.

Given a comma-separated values (CSV) string to a 2D array, using Javascript function.

Input: 'Name,Roll Number\nRohan,01\nAryan,02' 

Output:  [
             {Name: "Rohan", Roll Number: "01"},
             {Name: "Aryan", Roll Number: "02"}
        ]
// With delimiter ;    
    
Input: 'Name;Roll Number\nRohan;01\nAryan;02' 
        
Output:    [
             {Name: "Rohan", Roll Number: "01"},
             {Name: "Aryan", Roll Number: "02"}
        ]    

We must know some array and string prototype functions that will be helpful in this regard.

indexOf function: The String.prototype.indexOf() function finds the index of the first occurrence of the argument string in the given string and the value returned is in the 0-based index.

Example:

str = 'How\nare\nyou?' 

str.indexOf('\n');

Output:

3

Slice function: The Array.prototype.slice() method returns a new array containing a portion of the array on which it is implemented and the original array remains the same.

Example:

['a','b','c','d'].slice(1)

Output:

 ['b','c','d']

Map function: The Array.prototype.map() method returns a new array with the results of calling a provided function on every element.

Example:

arr = [2, 4, 8, 16]

// Dividing each element of the array by 2
newArr = arr.map( item => item/2) 

Output:

[1, 2, 4, 8]

Split function: The String.prototype.split() method is used to split the given string into an array of strings by separating it into substrings using a specified separator provided in the argument.

Example:

str = "Geeks for Geeks"

// Split the array when ' ' is located
arr = str.split(' ');

Output:

[ 'Geeks', 'for', 'Geeks' ]

Reduce function: The Array.prototype.reduce() method in JavaScript is used to reduce the array to a single value and executes a provided function for each element of the array from left to right and the return value of the function is stored in an accumulator.

Example:

 arr = [2,4,6,8]
 
 // Here 0 is the initial value of the accumulator
 // while traversing, currentValue has been added
 
 arr.reduce(function(accumulator,currentValue){
     return accumulator+currentValue;
 },0)

Output:

20

Approach:

• The JavaScript string slice() method extracts parts of a string and returns the extracted parts in a new string taking ‘\n’ as the first occurrence.
• Data Values are stored using “\n” as the delimiter.
• JavaScript map() function will iterate over all values of the title values array and append each object at the end of the array
• The “storeKeyValue” variable is used to store each key with its respective values.

Example: In this example, we will convert a comma-separated value (CSV) to a javascript array using the slice(), map(), split(), and reduce() methods of Javascript.

Javascript

<script>
    function CSVstring_to_Array(data, delimiter = ',') {

        /* This variable will collect all the titles
           from the data variable
           ["Name", "Roll Number"] */

        const titles = data.slice(0, data
            .indexOf('\n')).split(delimiter);

        /* This variable will store the values
           from the data
           [ 'Rohan,01', 'Aryan,02' ] */
        const titleValues = data.slice(data
            .indexOf('\n') + 1).split('\n');

        /* Map function will iterate over all
           values of title values array and
           append each object at the end of
           the array */
        const ansArray = titleValues.map(function (v) {

            /* Values variable will store individual
               title values
               [ 'Rohan', '01' ] */
            const values = v.split(delimiter);

            /* storeKeyValue variable will store
               object containing each title
               with their respective values i.e
               { Name: 'Rohan', 'Roll Number': '01' } */
            const storeKeyValue = titles.reduce(
                function (obj, title, index) {
                    obj[title] = values[index];
                    return obj;
                }, {});

            return storeKeyValue;
        });

        return ansArray;
    };

    var inputString1 = "Name,Roll Number\nRohan,01\nAryan,02";
    console.log(CSVstring_to_Array(inputString1));

    var inputString2 = "Name;Roll Number\nRohan;01\nAryan;02";
    console.log(CSVstring_to_Array(inputString2,';'));
</script>

Output: