freeCodeCamp/curriculum/challenges/chinese/10-coding-interview-prep/rosetta-code/identity-matrix.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
5a23c84252665b21eecc7eb1	Identity matrix	5	302290	identity-matrix

--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).

• \(\displaystyle I_{n}=\begin{bmatrix} 1 & 0 & 0 \cr 0 & 1 & 0 \cr 0 & 0 & 1 \cr \end{bmatrix}\)

--instructions--

Write a function that takes a number n as a parameter and returns the identity matrix of order \( n \times n \).

--hints--

idMatrix should be a function.

assert(typeof idMatrix == 'function');

idMatrix(1) should return an array.

assert(Array.isArray(idMatrix(1)));

idMatrix(1) should return [ [ 1 ] ].

assert.deepEqual(idMatrix(1), results[0]);

idMatrix(2) should return [ [ 1, 0 ], [ 0, 1 ] ].

assert.deepEqual(idMatrix(2), results[1]);

idMatrix(3) should return [ [ 1, 0, 0 ], [ 0, 1, 0 ], [ 0, 0, 1 ] ].

assert.deepEqual(idMatrix(3), results[2]);

idMatrix(4) should return [ [ 1, 0, 0, 0 ], [ 0, 1, 0, 0 ], [ 0, 0, 1, 0 ], [ 0, 0, 0, 1 ] ].

assert.deepEqual(idMatrix(4), results[3]);

--seed--

--after-user-code--

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 ] ]]

--seed-contents--

function idMatrix(n) {

}

--solutions--

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;
        })
    });
}