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

title, id, challengeType

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

- 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

console.info('after the test');

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;
		})
	});
}