PHP quickly gets random small arrays in large arrays

There is a function to guess what users like. Users can refresh the recommended content by clicking to change a group.

First query the database to get the first 1000 pieces of data, and then randomly remove 4 pieces.

After I finished writing the program, I found that it ran very slowly. Every time I refreshed it, I had to wait a long time for it to come out.

The code is as follows:

The above writing method must be sorted after using unset.

unset will only delete the key value, but the key will be retained.

The improved writing is as follows:

Efficiency increased by 3-4 times.