Question

What is the best way to randomize items in an array and also remove random items to get to a required array length?

Let’s say I have an array with 100 items.

First, I want to randomize it.

Then, I have three percent coefficients: 10%, 30%, 60%.

I want to remove items from the original array so the new array I get will be 60% of the original size (60 items), then 30%, then 10%.

Answer 1

The best way to randomise the array would be to use a Fisher-Yates-Durstenfeld shuffle. You could either do this in-place (ie, shuffle the existing array) or create a new collection containing the items in random order.

Here’s how I’d probably do it, creating a new shuffled collection rather than mutating the original array, and then using Skip and Take to get the required sub-sequences of the shuffled array. (And it would be easy enough to alter this code to perform an in-place shuffle instead, if you prefer.)

// uses Shuffle extension from https://stackoverflow.com/a/1653204/55847
var temp = original.Shuffle().ToArray();
var sixty = temp.Take((int)(temp.Length * 0.6)).ToArray();
var thirty = temp.Skip(sixty.Length).Take((int)(temp.Length * 0.3)).ToArray();
var ten = temp.Skip(sixty.Length + thirty.Length).ToArray();