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---
title: Vector dot product
id: 594810f028c0303b75339ad3
challengeType: 5
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forumTopicId: 302343
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---
## Description
< section id = 'description' >
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A vector is defined as having three dimensions as being represented by an ordered collection of three numbers: (X, Y, Z).
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< / section >
## Instructions
< section id = 'instructions' >
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Write a function that takes any numbers of vectors (arrays) as input and computes their dot product. Your function should return < code > null< / code > on invalid inputs such as vectors of different lengths.
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< / section >
## Tests
< section id = 'tests' >
```yml
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tests:
- text: dotProduct must be a function
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testString: assert.equal(typeof dotProduct, 'function');
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- text: dotProduct() must return null
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testString: assert.equal(dotProduct(), null);
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- text: dotProduct([[1], [1]]) must return 1.
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testString: assert.equal(dotProduct([1], [1]), 1);
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- text: dotProduct([[1], [1, 2]]) must return null.
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testString: assert.equal(dotProduct([1], [1, 2]), null);
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- text: dotProduct([1, 3, -5], [4, -2, -1]) must return 3.
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testString: assert.equal(dotProduct([1, 3, -5], [4, -2, -1]), 3);
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- text: < code > dotProduct(...nVectors)</ code > should return 156000
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testString: assert.equal(dotProduct([ 0, 1, 2, 3, 4 ], [ 0, 2, 4, 6, 8 ], [ 0, 3, 6, 9, 12 ], [ 0, 4, 8, 12, 16 ], [ 0, 5, 10, 15, 20 ]), 156000);
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```
< / section >
## Challenge Seed
< section id = 'challengeSeed' >
< div id = 'js-seed' >
```js
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function dotProduct(...vectors) {
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// Good luck!
}
```
< / div >
< / section >
## Solution
< section id = 'solution' >
```js
function dotProduct(...vectors) {
if (!vectors || !vectors.length) {
return null;
}
if (!vectors[0] || !vectors[0].length) {
return null;
}
const vectorLen = vectors[0].length;
const numVectors = vectors.length;
// If all vectors not same length, return null
for (let i = 0; i < numVectors ; i + + ) {
if (vectors[i].length !== vectorLen) {
return null; // return undefined
}
}
let prod = 0;
let sum = 0;
let j = vectorLen;
let i = numVectors;
// Sum terms
while (j--) {
i = numVectors;
prod = 1;
while (i--) {
prod *= vectors[i][j];
}
sum += prod;
}
return sum;
}
```
< / section >