Get column from a two dimensional array

How can I retrieve a column from a 2-dimensional array and not a single entry? I'm doing this because I want to search for a string in one of the columns only so if there is another way to accomplish this please tell me.

I'm using the array defined this way:

var array=[];

At the end the size of this array is 20(col)x3(rows) and I need to read the first row and check the existence of some phrase in it.

Solution 1:

Taking a column is easy with the map function.

// a two-dimensional array
var two_d = [[1,2,3],[4,5,6],[7,8,9]];

// take the third column
var col3 = two_d.map(function(value,index) { return value[2]; });

Why bother with the slice at all? Just filter the matrix to find the rows of interest.

var interesting = two_d.filter(function(value,index) {return value[1]==5;});
// interesting is now [[4,5,6]]

Sadly, filter and map are not natively available on IE9 and lower. The MDN documentation provides implementations for browsers without native support.

Solution 2:

Use Array.prototype.map() with an arrow function:

const arrayColumn = (arr, n) => arr.map(x => x[n]);

const twoDimensionalArray = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];

console.log(arrayColumn(twoDimensionalArray, 0));

Note: Array.prototype.map() and arrow functions are part of ECMAScript 6 and not supported everywhere, see ECMAScript 6 compatibility table.