# How to emulate any load profile with simple random() function in JavaScript or any other language

# TL;DR

When you have a list of items, for example: [a, b, c], and you want to get, for example, a linear distribution of them with usual .random() function then simply make a number of items in that list in linear distribution: [a, b, b, c, c, c] and then get .random() from this new list — and you’ll get the result in linear distribution:

You can make harder angle or softer angle by adding more or less items for each next step, for example:

- Softer than 45*: [a, b, c, c]
- Exactly 45*: [a, b, b, c, c, c]
- Harder than 45*: [a, b, b, b, c, c, c, c, c, c]

And this is applied not only for linear, but for any type of profiles: normal distribution, exponent, square, etc. — every profile, every curve could be emulated with a simple .random() function.

# How I came to this

I develop Product Analytics app and it has demo mode. And it has sankey (tree) chart. But when I flushed the chart with .random() data, it looked stupid, unreal and not interesting — every branch height was about the same (which means: used the same compared to each other):

I wanted to have a normal distribution for that chart to make some items narrow, another items wide — to be more interesting to look at and play with. But there’s no built-in function for normal distribution in Vanilla JavaScript. Instead — a long discussion thread on StackOverflow.

Looking at the normal distribution chart plot I eventually came to an idea, that these vertical bars represent repetition of the X values. And this means that instead of having only one value for each X in array I can have N values for each X in array and then pass .random() function among elements of that array — and I will get what I want: random, but in a form I wanted.

So, I made this modification — I increased number of elements:

- original list: [a, b, c, d, e]
- normal distribution list: [a, b, b, c, c, c, c, c, d, d, e]

And it worked:

See? How much interesting this chart compared to original .random() one!

And if we put data in a table a sort values from max to min, then we’ll see that hals of the “bell curve” of normal distribution:

A half of curve because of sorting: it brings everything on one side, making original curve as twice as wide.

That’s why when I wanted to simulate users and I wanted to make linear simulation, I made simulation the same way and got this:

And all together, the whole picture now looks like this:

- normal distribution for sankey (tree) chart and a table below on the left side,
- linear distribution for UserIDs in the center,
- and constant simple .random() distribution in time on the right:

And all these are made by simple and the same, single .random() function.

# Source code for JavaScript

# Bonus

Only for those who read till the end!

As arrays could be complex and heavy, multiplication of their elements could cost you a lot in terms of RAM consumption. That’s why instead of multiplication of the elements themselves, multiply their IDs:

- original: [a, b, c]
- linear “bad practice”: [a, b, b, c, c, c]
- linear “good practice”: [0, 1, 1, 2, 2, 2] — ID’s for a, b and c

and get .random() from IDs array and then get the original element from original array by that ID.

Hope you liked it and had fun!