Javascript: Generate random number using a range inside a range

Question

I am trying to make a number simulation that functions as follows:

Begins at baseline value
Generates random value within given range of baseline
Takes generated value and generate another value within same range
All generated values remain within a larger range

So if I have a starting value of 5, I need it to generate a number within a range of say 2. It then needs to take that value (between 3 and 7) and generate another number with the same range of 2, and so on. But I also need any numbers generated to stay between 0 and 10.

I can use random() with a single defined range, but I don't know how to do two:

function generateValue(min, max) {
    var max = 2,
        min = 0,
        value = (Math.random() * (max - min) + min).toFixed(6);
    return value;
}

don't understand 4. because all generated values already within the salll range,so they surely within a larger range — xianshenglu
– xianshenglu, Commented Feb 10, 2018 at 1:19
Give an example of what you get and what expect. Those 1.2.3.4. are not very clear :) — RaphaMex
– RaphaMex, Commented Feb 10, 2018 at 1:25
So if I have a starting value of 5, I need it to generate a number within a range of say 2. It then needs to take that value (between 3 and 7) and generate another number with the same range of 2, and so on. But I also need any numbers generated to stay between 0 and 10. Does that make sense? — Ethameshep
– Ethameshep, Commented Feb 10, 2018 at 1:50
Also you use .toFixed(6), which means you want to return a string with 6 decimals? If you want to chain call your function, better return a number no? — RaphaMex
– RaphaMex, Commented Feb 10, 2018 at 2:17

Boris Lobanov · Accepted Answer · 2018-02-10 01:59:57Z

2

You need a function that accepts 4 arguments: baseline, range, min and max (if I understand you correctly). Also, I believe you had a mistake in you formula for getting a random number from a range. Here's a function that does what you need, I think:

function generateValue(baseline, range, min, max) {
    let localMin = Math.max(baseline - range, min);
    let localMax = Math.min(baseline + range, max);

    return (Math.random() * (localMax - localMin) + localMin).toFixed(6);
}

answered Feb 10, 2018 at 1:59

Boris Lobanov

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RaphaMex · Accepted Answer · 2018-02-10 02:14:12Z

0

Here is your function. Its parameter is the baseline value. You can make min, max, range parameters too if you wish:

function generateValue(value) {
    let max = 10,
        min = 0,
        range = 2,
        newValue = value; // Start at baseline value
    newValue += (2 * Math.random() - 1) * range; // Generate new value within +/- range
    return (newValue < min ? min : // Cannot be lower than min
            newValue > max ? max : // Cannot be greater than max
            newValue);
}

answered Feb 10, 2018 at 2:14

RaphaMex

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