Sorting arrays numerically

问题

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?

回答1:

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;
}

回答2:

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.

回答3:

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

usort($myarray, "sortByCount");

来源：https://stackoverflow.com/questions/1818514/sorting-arrays-numerically

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sorting