PHP custom sorting

Question

I'm trying to sort an array of values.

The possible values in the array are 'neg_infinity',... {real numbers},.., 'infinity'

<?php
$a = array(
  array('column' => 3),
  array('column' => -1),
  array('column' => 1),
  array('column' => .1),
  array('column' => 2),
  array('column' => 'infinity'),
  array('column' => 'neg_infinity'),
  array('column' => 'infinity'),
);

I want:

    $a = array(
      array('column' => 'neg_infinity'),
      array('column' => -1),
      array('column' => .1),
      array('column' => 1),
      array('column' => 2),
      array('column' => 3),
      array('column' => 'infinity'),
      array('column' => 'infinity'),
    );

I've been playing around with uasort.

Anybody have a solution to his problem?

TEST DRIVER

<?php
function cmp($a, $b) {
    if ($a == $b) {
        return 0;
    }
    if ($a == 'neg_infinity') {
        return -1;
    }
    if ($a == 'infinity') {
        return 1;
    }
    return ($a < $b) ? -1 : 1;
}

$a = array('a' => 'infinity', 'b' => 8, 'c' => -1,'e' => 2, 'f' => 5, 'g' => 3, 'h' => -4, 'd' => 'neg_infinity');


uasort($a, 'cmp');


var_dump($a);

What did you try? Post your example and we can probably tell you why you failed. — Evert
– Evert, Commented Aug 31, 2011 at 20:08

Marc B · Accepted Answer · 2011-08-31 20:12:06Z

5

Use this for your sorting function:

function cmp($a, $b) {
    if ($a == 'neg_infinity') {
       return -1
    }
    if ($a == 'infinity') {
       return 1
    }
    return ($a < $b ? -1 : 1)
}

answered Aug 31, 2011 at 20:12

Marc B

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5 Comments

Sam Dufel Over a year ago

What if both $a and $b == 'infinity'?

Marc B Over a year ago

Then the a value will take priority. If you want that to be different (or randomized), you'll have to add an extra clause to handle the case. It's the same if a == b, the a value will take priority.

Yada Over a year ago

I actually came up with this solution as well. But it doesn't work.

Marc B Over a year ago

Hm.. didn't notice you've actually got a multidimensional array. You'd want to use if ($a['column'] == 'neg_infinity') and the like instead. Otherwise you're directly comparing arrays to strings/integers, which'll fail.

dierre Over a year ago

@Marc B: you need to check $b too, otherwise you're gonna miss the comparison when 'infinity' is $b

mfonda · Accepted Answer · 2011-08-31 20:13:01Z

5

Something like this should work:

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

answered Aug 31, 2011 at 20:13

mfonda

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2 Comments

animuson Over a year ago

Do you really need the first conditional?

mfonda Over a year ago

@animuson: Maybe not, but per the docs, "The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second."

dierre · Accepted Answer · 2011-08-31 20:49:25Z

1

You tricky bastard! I'll give you plus one because it took me 20 minutes to get it was an array of arrays.

function cmp($a, $b) {
    if ($a['column'] == 'neg_infinity') {
        return -1;
    }
    if ($a['column'] == 'infinity') {
        return 1;
    }

    if ($b['column'] == 'neg_infinity') {
        return 1;
    }
    if ($b['column'] == 'infinity') {
        return -1;
    }
    if ($a['column'] == $b['column']) {
        return 0;
    }
    return ($a['column'] < $b['column']) ? -1 : 1;
}

it is tested: http://codepad.org/13GuICbH

IdeOne is too mainstream, ya know.

answered Aug 31, 2011 at 20:49

dierre

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2 Comments

Yada Over a year ago

Thanks. I forgot to check the $b values.

dierre Over a year ago

It slipped from me too at the beginning but at a certain point you're going to compare -1 and neg_infinity for sure and if you don't check $b you miss that comparison.

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