How does usort work

Improve this answer. I should've seen that. Yep, the compare function always takes two arguments. Add a comment. In the PHP docs they say PHP versions below 7 have the limits to , but they don't clearly lay it out like you did. Your explanation would have made the docs much clearer! Paul Paul k 25 25 gold badges silver badges bronze badges. Usort uses counting sort and not quick sort. Check this ijest.

PHP's usort is implemented with Quicksort. See the note in the link. Mahendra Jella Mahendra Jella 4, 1 1 gold badge 29 29 silver badges 36 36 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? The usort function in PHP sorts a given array by using a user-defined comparison function.

This function is useful in case if we want to sort the array in a new manner. This function assigns new integral keys starting from zero to the elements present in the array and the old keys are lost. This function returns an integer value based on the following conditions. If two arguments are equal, then it returns 0, If first argument is greater than second, it returns 1 and if first argument is smaller than second, it returns Return Value: This function returns the boolean type of value.

Below program illustrate the usort function in PHP:. Previous Sort array of objects by object fields in PHP. Next PHP pos Function. Recommended Articles. Posts: 57 Threads: 1 Joined: Nov Reputation: 6. Hi, this is pretty simple, is it not? Quote: The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

Which can lead to unpredictable results. If you want to sort based on that rank, you should compare the values, not subtract them, as in: PHP Code:. Narf Me. Posts: 1, Threads: 1 Joined: Oct Reputation: The term "weight" is often used to describe similar values in sorting algorithms, so I'll use it here as well Thank you for those explanations, they help a lot.

So does usort reiterate again and again until the entire list remains unchanged? If it does it sounds like it might cause some overhead although so far I can't detect any noticeable delay so it must be really fast at it. Thanks again for the above answers, I really appreciate the explanations. Best wishes, Paul. How it works is that it splits up the array into the smallest unit, so, 1 element of the array.

Then it compares each element with the adjacent list, and merges the values. It is faster than bubble sort on large unsorted lists, but if the list is already sorted, bubble sort will be faster than merge sort. Finally I get it. That was an excellent link, thank you.