Functional Programming in PHP by Simon Holywell

Author:Simon Holywell [Simon Holywell]
Language: eng
Format: epub
Tags: Core Programming
Publisher: php[architect]
Published: 2016-11-02T04:00:00+00:00

At the other end of the equation we have tail that will return a list with all but the first value in the array contained in it.

function tail(array $arr) { return array_slice($arr, 1); } tail([1,2,3,4,5]); // [2,3,4,5]

These two functions can be used together to work through a list using recursion.

function print_items(array $arr) { echo head($arr) . '-'; if(tail($arr)) print_items(tail($arr)); } print_items([1,2,3,4,5]); // 1-2-3-4-5-

6.2 Flattening lists

Lists of lists can be very helpful when dealing with complex datasets or when transforming an array via array_map() where it would return an array from the applied function. In some instances though, you have a list of lists that really should just be one list with all values at the top level. The problem could look something like:

$arr = [1, 2, 3, 4, 5]; $divisor = 10.5; $arr2 = array_map(function($x) use ($divisor) { return [$x, $x / $divisor, $x % $divisor]; }, $arr); // [ // [1, 0.095238095238095233, 1], // [2, 0.19047619047619047, 2], // [3, 0.2857142857142857, 3], // [4, 0.38095238095238093, 4], // [5, 0.47619047619047616, 5] // ]

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