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title	id	challengeType	forumTopicId
Identity matrix	5a23c84252665b21eecc7eb1	5	302290

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 \( n \times n \).

Tests

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

Challenge Seed

function idMatrix(n) {

}

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;
		})
	});
}

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