freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/rosetta-code/identity-matrix.english.md

title	id	challengeType
Identity matrix	5a23c84252665b21eecc7eb1	5

Description

An identity matrix is a square matrix of size \( n \times n \), where the diagonal elements are all 1s (ones), and all the other elements are all 0s (zeroes). \begin{bmatrix} 1 & 0 & 0 \cr 0 & 1 & 0 \cr 0 & 0 & 1 \cr \end{bmatrix} Write a function that takes a number 'n' as a parameter and returns the identity matrix of order n x n.

Instructions

Tests

tests:
  - text: <code>idMatrix</code> should be a function.
    testString: assert(typeof idMatrix=='function','<code>idMatrix</code> should be a function.');
  - text: <code>idMatrix(1)</code> should return an array.
    testString: assert(Array.isArray(idMatrix(1)),'<code>idMatrix(1)</code> should return an array.');
  - text: <code>idMatrix(1)</code> should return <code>'+JSON.stringify(results[0])+'</code>.
    testString: assert.deepEqual(idMatrix(1),results[0],'<code>idMatrix(1)</code> should return <code>'+JSON.stringify(results[0])+'</code>.');
  - text: <code>idMatrix(2)</code> should return <code>'+JSON.stringify(results[1])+'</code>.
    testString: assert.deepEqual(idMatrix(2),results[1],'<code>idMatrix(2)</code> should return <code>'+JSON.stringify(results[1])+'</code>.');
  - text: <code>idMatrix(3)</code> should return <code>'+JSON.stringify(results[2])+'</code>.
    testString: assert.deepEqual(idMatrix(3),results[2],'<code>idMatrix(3)</code> should return <code>'+JSON.stringify(results[2])+'</code>.');
  - text: <code>idMatrix(4)</code> should return <code>'+JSON.stringify(results[3])+'</code>.
    testString: assert.deepEqual(idMatrix(4),results[3],'<code>idMatrix(4)</code> should return <code>'+JSON.stringify(results[3])+'</code>.');

Challenge Seed

function idMatrix (n) {
  // Good luck!
}

After Test

let results=[[ [ 1 ] ],
[ [ 1, 0 ], [ 0, 1 ] ],
[ [ 1, 0, 0 ], [ 0, 1, 0 ], [ 0, 0, 1 ] ],
[ [ 1, 0, 0, 0 ], [ 0, 1, 0, 0 ], [ 0, 0, 1, 0 ], [ 0, 0, 0, 1 ] ]]

Solution

function idMatrix (n) {
	return Array.apply(null, new Array(n)).map(function (x, i, xs) {
		return xs.map(function (_, k) {
			return i === k ? 1 : 0;
		})
	});
}