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How to convert a 2D array to a comma-separated values (CSV) string in JavaScript ?

  • Last Updated : 26 Apr, 2021

Given a 2D array, we have to convert it to a comma-separated values (CSV) string using JS.

Input:
[ [ "a" , "b"] , [ "c" ,"d" ] ]
Output:
"a,b 
 c,d"
Input:
[ [ "1", "2"]
["3", "4"]
["5", "6"] ]
Output:
"1,2
3,4
5,6"

To achieve this, we must know some array prototype functions which will be helpful in this regard:

Join function: The Array.prototype.join( ) function is used to join all the strings in an array with a character/string.

Example:

[ "a","b"].join( ",") will result in : "a,b"

Map function: The Array.prototype.map() returns a new array with the results of calling a function which we provide, on each element.



Example:

arr= ["a","b"]

// Adding "c" to each element
newArray = arr.map( item => item + "c") 
value of newArray = ["ac", "bc"]

Approach: We will use the map function and join function to combine each 1D row into a string with the separation of a comma. and then join all the individual strings with “\n”, using the join function.

Example:

Javascript




<script>
// Create CSV file data in an array  
var array2D = [ 
                [ "a" , "2"] ,
                [ "c" ,"d"
              ];
  
// Use map function to traverse on each row
var csv = array2D
  .map((item) => {
    
    // Here item refers to a row in that 2D array
    var row = item;
      
    // Now join the elements of row with "," using join function
    return row.join(",");
  }) // At this point we have an array of strings
  .join("\n");
    
  // Join the array of strings with "\n"
console.log(csv);
</script>

Output:

a,2
c,d

Explanation: We first used the map function on the 2D array to traverse on each row, then we used the join function to join the array of elements in that row using a comma. Next, that map function returns an array of strings, which we join by using “\n”.  Thus resulting in a CSV string.

Alternative Approach: We can even use for loops to traverse in the array, instead of a map.

Example:

Javascript




<script>
var csv="";
create CSV file data in an array  
var array2D = [ 
                [ "a" , "2"] ,
                [ "c" ,"d"
              ];
  
for (var index1 in array2D) {
  var row = array2D[index1];
    
  // Row is the row of array at index "index1"
  var string = "";
    
  // Empty string which will be added later
  for (var index in row) {
    // Traversing each element in the row
    var w = row[index];
      
    // Adding the element at index "index" to the string
    string += w;
    if (index != row.length - 1) {
      string += ",";
      // If the element is not the last element , then add a comma
    }
  }
  string += "\n";
    
  // Adding next line at the end
  csv += string;
  // adding the string to the final string "csv"
}
console.log(csv);
</script>
Output:
a,2
c,d



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