Sorting Array using usort?

Question

I am having problem trying to sort an array - I want all the IsOpen = 1 to appear at the top?

Example:

Array
(
    [0] => Array
        (
            [Isopen] => 0
        )

    [2] => Array
        (
            [Isopen] => 1
        )

    [3] => Array
        (
            [Isopen] => 0
        )

    [4] => Array
        (
            [Isopen] => 1
        )

Code:

   function cmp($a, $b) {
        if ($a['Isopen'] >= $b['Isopen']) {
            return 0;
        }
    }

    usort($data['rowResult'], "cmp");

I don't understand what does $a and $b mean, I had a look at the PHP documentation - information is not clear.

SERPRO · Accepted Answer · 2011-11-15 10:01:49Z

3

$a and $b are the elements to compare:

function cmp($a, $b) {
    if ($a['Isopen'] == $b['Isopen']) {
        return 0;
    }
    return ($a['Isopen'] > $b['Isopen']) ? -1 : 1;
}

edited Nov 15, 2011 at 10:01

answered Nov 14, 2011 at 16:50

SERPRO

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3 Comments

I'll-Be-Back Over a year ago

It appear all the $b['Isopen'] = 1 is at the bottom. Should other way around

SERPRO Over a year ago

are you sure you copy that function? check the < on the last return, in case you put >

I'll-Be-Back Over a year ago

Changed from < to > fixed the problem

plandolt · Accepted Answer · 2011-11-14 16:50:18Z

1

The cmp funciton should return 0, -1 (or less than zero) or 1 (or greater than zero).

zero if the two values are equal.
greater than zero if the value form a is higher.
less than zero if the value from b is higher.

for the comparison of the two values you may use php function strcmp

function cmp($a, $b) {
  return strcmp($a['Isopen'], $b['Isopen']);
}

answered Nov 14, 2011 at 16:50

plandolt

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Comments

confucius · Accepted Answer · 2011-11-14 16:54:27Z

1

function cmp($a, $b) {
        if ($a['Isopen'] == $b['Isopen']) {
            return 0;
        }
        return ($a['Isopen'] >  $b['Isopen']) ? -1 : 1;
    }

this will makes Isopen = 1 at the end of the array if you want it at the begging make this

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

answered Nov 14, 2011 at 16:54

confucius

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1 Comment

I'll-Be-Back Over a year ago

To make Isopen at the top, I have to change it to: return ($a['Isopen'] < $b['Isopen']) ? 1 : -1; seem to work

Jay Merritt · Accepted Answer · 2011-11-14 16:48:39Z

0

in this example $a[] and $b[] are two arrays that are handed to the function named 'cmp'. it compares the value of 'Isopen' in two different arrays.

check out the documentation on user defined functions http://php.net/manual/en/language.functions.php

and how to properly use usort() http://php.net/manual/en/function.usort.php

answered Nov 14, 2011 at 16:48

Jay Merritt

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Comments

John Cartwright · Accepted Answer · 2011-11-14 16:49:22Z

0

The sorting aglorithm is a Bubble Sort.

Essentially, it compares array entities at a time to determining their ordering. To see a step by step example, see http://en.wikipedia.org/wiki/Bubble_sort#Step-by-step_example

answered Nov 14, 2011 at 16:49

John Cartwright

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2 Comments

Erbureth Over a year ago

Why reinvent the wheel when he can use library function? And why the slow bubble sort of all algorithms?

John Cartwright Over a year ago

@Erbureth Who said anything about reinventing the wheel? I simply provided documentation on how the sort is actually performed, i.e., the algorithm.

Igor Parra · Accepted Answer · 2011-11-14 16:57:42Z

0

Your function cmp is not correct (see my example of correct use). Besides if you use php 5.3+ you can use anonymous functions like this:

usort($data['rowResult'], function($a, $b)
{
    if ($a['Isopen'] == $b['Isopen'])
    {
        return 0;
    }

    return $a['Isopen'] < $b['Isopen'] ? -1 : 1;
});

answered Nov 14, 2011 at 16:57

Igor Parra

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