Sorting arrays numerically

Question

I have a PHP array that I need to sort. I have included the example array below. I need to put the top 10 number of URLS plus their perspective counts in a different array. I know I could run into problem if there aren't 10 top matches ... if that happens then a random matching would be fine.

Any suggestions?

I have tried sort(myarray) but that just sorts the first object in the array I need it to sort the second.

Any ideas?

you want to sort them on the count field i presume? – NDM Nov 30 '09 at 08:31 — NDM, Nov 30 '09 at 08:31

score 2 · Accepted Answer · answered Nov 30 '09 at 08:30

2

You need to write a custom sorting function - like this:

function MyCustomSort($a, $b)
{
    if ($a->count == $b->count) {
        return 0;
    }
    return ($a->count < $b->count) ? -1 : 1;
}

Then you pass that function into a sort - like this:

usort($myArray, "MyCustomSort");

You could also write a function to help you sort by website - like this:

function MyCustomSort($a, $b)
{
    if ($a->name == $b->name) {
        return 0;
    }
    return ($a->name < $b->name) ? -1 : 1;
}

answered Nov 30 '09 at 08:30

Fenton

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Awesome thanks! I assume that switching "-1 : 1" in the above code to "1 : -1" will reverse the order? Yup tried it that worked to reserve it. Thanks. – Adam Evers Nov 30 '09 at 08:35
Yes - although I usually change the less than (<) to be greater than (>) to get the same effect! – Fenton Nov 30 '09 at 08:42

NDM · Answer 2 · 2009-11-30T13:39:48.903

0

function sortByCount($a, $b)
{
    if ($a['count'] == $b['count']) {
        return 0;
    }
    return ($a['count'] < $b['count']) ? -1 : 1;
}

usort($myarray, "sortByCount");

edited Nov 30 '09 at 13:39

answered Nov 30 '09 at 08:32

NDM

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In your usort function, you've called the wrong sort function - "cmp" should be "sortByCountp", which is what you've called the function. – Fenton Nov 30 '09 at 08:41

score 0 · Answer 3 · answered Nov 30 '09 at 11:42

You may use decorate-sort-undecorate pattern.

<?php

$arr = Array
(
    [0] => Array
        (
            [name] => http://bit.ly/2oUTzf
            [count] => 1
        )

    [1] => Array
        (
            [name] => http://tiny.cc/wyNbi
            [count] => 1
        )

    [2] => Array
        (
            [name] => http://ow.ly/Almo
            [count] => 1
        )

    [3] => Array
        (
            [name] => http://bit.ly/7bQ8sY
            [count] => 1
        )
...
);

// actual sorting below
$arr= array_map(create_function('$a', 'return array($a["count"], $a);'), $arr); // transform into array of arrays consisted of sort key and item
sort($arr); // sort array of arrays
$arr = array_map('end', $arr); // take only last element from each array

print_r($arr);

How does it work?

Instead of sorting array of your items you sort array of arrays whose last element is item and first is the key by which you want to sort. After sorting you keep only the item.

You can use just sort for sorting array of arrays because PHP compares two same length arrays by comparing its elements one by one.

Sorting by multiple fields

You may use more then one sort key, for example sort by count and if counts are identical take url into account. You can do this by decorating with multiple keys with order of importance like so:

$arr = array_map(create_function('$a', 'return array($a["count"], $a["name"], $a);'), $arr);

Why it's fast

This way might be faster that using usort because it calls your custom code only n-times for sorting array of length n. Comparisons during sort are done using built in comparator so should be fast. In usort method custom comparator is called multiple times (more than n times) during sort and it may slow down things.

Sorting arrays numerically

3 Answers3

How does it work?

Sorting by multiple fields

Why it's fast

Linked