83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
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---
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title: Identity matrix
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id: 5a23c84252665b21eecc7eb1
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challengeType: 5
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---
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## Description
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<section id='description'>
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An <i>identity matrix</i> is a square matrix of size \( n \times n \),
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where the diagonal elements are all <b>1</b>s (ones),
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and all the other elements are all <b>0</b>s (zeroes).
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\begin{bmatrix} 1 & 0 & 0 \cr 0 & 1 & 0 \cr 0 & 0 & 1 \cr \end{bmatrix}
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Write a function that takes a number 'n' as a parameter and returns the identity matrix of order n x n.
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</section>
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## Instructions
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<section id='instructions'>
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</section>
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## Tests
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<section id='tests'>
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```yml
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- text: '''<code>idMatrix</code> should be a function.'''
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testString: 'assert(typeof idMatrix==''function'',''<code>idMatrix</code> should be a function.'');'
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- text: '''<code>idMatrix(1)</code> should return an array.'''
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testString: 'assert(Array.isArray(idMatrix(1)),''<code>idMatrix(1)</code> should return an array.'');'
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- text: '''<code>idMatrix(1)</code> should return <code>''+JSON.stringify(results[0])+''</code>.'''
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testString: 'assert.deepEqual(idMatrix(1),results[0],''<code>idMatrix(1)</code> should return <code>''+JSON.stringify(results[0])+''</code>.'');'
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- text: '''<code>idMatrix(2)</code> should return <code>''+JSON.stringify(results[1])+''</code>.'''
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testString: 'assert.deepEqual(idMatrix(2),results[1],''<code>idMatrix(2)</code> should return <code>''+JSON.stringify(results[1])+''</code>.'');'
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- text: '''<code>idMatrix(3)</code> should return <code>''+JSON.stringify(results[2])+''</code>.'''
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testString: 'assert.deepEqual(idMatrix(3),results[2],''<code>idMatrix(3)</code> should return <code>''+JSON.stringify(results[2])+''</code>.'');'
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- text: '''<code>idMatrix(4)</code> should return <code>''+JSON.stringify(results[3])+''</code>.'''
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testString: 'assert.deepEqual(idMatrix(4),results[3],''<code>idMatrix(4)</code> should return <code>''+JSON.stringify(results[3])+''</code>.'');'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function idMatrix (n) {
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// Good luck!
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}
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```
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</div>
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### After Test
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<div id='js-teardown'>
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```js
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console.info('after the test');
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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function idMatrix (n) {
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return Array.apply(null, new Array(n)).map(function (x, i, xs) {
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return xs.map(function (_, k) {
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return i === k ? 1 : 0;
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})
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});
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}
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```
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</section>
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