Efficiently pick n random elements from PHP array (without shuffle)

Question

I have the following code to pick $n elements from an array $array in PHP:

shuffle($array);
$result = array_splice($array, 0, $n);
         


        

Answer 1

This will only show benifits for small n compared to an array shuffle, but you could

1. Choose a random index r n times, each time decreasing the limit by 1
2. Adjust for previously used indices
3. Take value
4. Store used index

Pseudocode

arr = []
used = []
for i = 0..n-1:
    r = rand 0..len-i
    d = 0
    for j = 0..used.length-1:
        if r >= used[j]:
            d += 1
    arr.append($array[r + d])
    used.append(r)
return arr