Generate arrays with random numbers in javascript

Question

I need to create an array (observations) which contains arrays of eight numbers (named observation). These numbers should be in range between 0 and 9.

let observations = [];
let observation = [];
let min = 0;
let max = 9;
for (let i = 0; i < 20000; i++) {
    for (let j = 0; j < 8; j++) {
        observation[j] = Math.floor(Math.random() * (max - min + 1)) + min;
    }
    observations.push(observation);
}

Problem: The numbers are pseudo random and I get the same result 20 000 times.

Is there a possibility to fix this issue in JavaScript?

Barmar · Accepted Answer · 2018-10-12 22:09:29Z

2

You're reusing the same observation array each time, but simply overwriting it in the inner loop. So all the references to it contain the results from the last iteration.

You need to create a new observation array each time through the outer loop.

let observations = [];
let min = 0;
let max = 9;
for (let i = 0; i < 20000; i++) {
    let observation = [];
    for (let j = 0; j < 8; j++) {
        observation.push(Math.floor(Math.random() * (max - min + 1)) + min);
    }
    observations.push(observation);
}

answered Oct 12, 2018 at 22:09

Barmar

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Comments

Unmitigated · Accepted Answer · 2018-10-12 22:52:00Z

2

You could move the empty array inside of the first level, because you keep the same object reference.

let observations = [];
let min = 0;
let max = 9;
for (let i = 0; i < 20000; i++) {
    let observation = [];
    for (let j = 0; j < 8; j++) {
        observation[j] = Math.floor(Math.random() * (max - min + 1)) + min;
    }
    observations.push(observation);
}

edited Oct 12, 2018 at 22:52

Unmitigated

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answered Oct 12, 2018 at 22:09

Nina Scholz

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Comments

serginhofogo · Accepted Answer · 2018-10-12 22:38:52Z

0

Math.seed = function(s) {
    return function() {
        s = Math.sin(s) * 10000; return s - Math.floor(s);
    };
};

let observations = [];
let observation = [];
let min = 0;
let max = 9;
for (let i = 0; i < 20000; i++) {
        var d = new Date();
        var n = d.getMilliseconds();
    for (let j = 0; j < 8; j++) {
        observation[j] = Math.floor(Math.seed(i+j+n)() * (max - min + 1)) + min;
    }
    observations.push(observation);
    observation = [];
}

JSON.stringify(observations);

answered Oct 12, 2018 at 22:38

serginhofogo

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Comments

marzelin · Accepted Answer · 2018-10-12 23:00:23Z

0

A functional solution:

const observations = Array.from({length: 20000}, () => 
  Array.from({length: 10}, () => (Math.random() * 10 | 0)))

answered Oct 12, 2018 at 23:00

marzelin

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