[SOLVED] Sorting an 'array of arrays' by one index?

[teamv]

Hi all,

 

I have a large array filled with other arrays, each of which is slightly different, but they all have an index "time" which is a unix timestamp. Is there any easy function which will sort this arrays of array for me by that time index (highest to lowest), or will I have to use some kind of more complex recursive algorithm?  Would greatly appreciate any advice people can offer me on this question.

 

Thanks in advance for any and all suggestions.

 

Richard

[nikefido]

usort, uksrt, uasort. (check out php.net for usage/examples)

www.php.net/usort - basic sorting function

www.php.net/uasort - maintains index association

www.php.net/uksort - sort based on keys

 

There will take your array and a user-defined function and sort your multi-dim. arrays

 

typical user defined functions might be something like:

function mySort1 ($x, $y) {
    return ($x['key1'] > $y['Key1']);
}

 

and you implement it like:

usort($array, 'mySort1');//usort provides the function arguments

[GingerRobot]

Try:

 

<?php
function mysort($a,$b){
return $a['time'] - $b['time'];
}
uasort($yourarray,'mysort');
?>

[teamv]

Thank you so much for the quick responses! I will have a go at implementing the above examples and let you both know how it goes.

[teamv]

Thank guys, it worked perfectly! I used:

 

// function to sort the array by time
function mysort($a,$b){
	return $a['time'] < $b['time'];
}

// sort the array
uasort($array,'mysort');

 

Thanks again!

[Barand]

I'd be wary of relying on that solution.

 

Your function only returns true or false. whereas usort() etc require the custom function should return a negative , zero or a positive result (as GingerRobot's does) depending on whether A should sort above, is equal to, or should sort below B

[teamv]

Thank you for the advice, so to clarify I should change uasort to usort instead?

[Barand]

No.

 

I'm saying your mysort() function is wrong and should be like GingerRobots

[teamv]

No.

 

I'm saying your mysort() function is wrong and should be like GingerRobots

 

Oh, well I did try theirs first but it was sorted in the opposite order than I wanted. I then tried changing the - to a + sign as I expected that to switch it round, but it didn't. What I am missing?

 

Thanks for all your help support thus far!

[GingerRobot]

You need to switch the variables around, rather than the sign.

 

<?php
function mysort($a,$b){
return $b['time'] - $a['time'];
}
uasort($yourarray,'mysort');
?>

[Barand]

to switch the sign to give a DESC sort

 

return -($a['time'] - $b['time']);

 

which resolves to

 

return ($b['time'] - $a['time']);      (as GR states above)

[teamv]

Ah that makes a lot more sense than a plus sign , I should have tried to think through the logic of what was happening in the function rather than just making a change like I did, sorry. I have now made the changes given above though and all is working well!

 

Well thanks for sticking with me guys, and for all your help. You've been great!

 

Richard