21.3. Sorting with a Comparison Function
The built-in sorting functions are appropriate in the overwhelming majority of situations. If your problem requires a sort that performs better than the one used in the built-in functions, you are faced with coding your own. If your problem is that you need to compare complex elements, such as objects or multidimensional arrays, the solution is to write a comparison function and plug it into the usort function.
The usort function allows you to sort an array using your own comparison function. Your comparison function must accept two values and return an integer. The two arguments are compared, and if a negative number is returned, then the values are considered to be in order. If zero is returned, they ...
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