I’ve blogged twice recently about sorting an array of structures in ColdFusion, using both pure CF, and dipping into Groovy. This time we’ll look at how we can easily do the same task in PHP. In this post I will take the same problem, a complex array containing a structure (in PHP, an associative array), and sort it. The sort criteria in this case is that if the product IDs are the same, we compare the prices of the products and sort there. So we have a two-level sort: Product ID, then price.
To do this in PHP the method usort will come in handy. The usort method takes two parameters. The first parameter is the array to be sorted (passed by reference, so make sure you keep a copy if you need the original), and a function to compare two items.
The comparator function simply takes two items. It is up to us to compare them how we like, and return zero (0) for equal, one (1) for the first item being greater (or after) the second item, or negative one (-1) for the first item coming before the second item, or less than. Let’s take a look at how that function would work.
<?php
function comparator($a, $b) {
$productId1 = $a["productId"];
$productId2 = $b["productId"];
$price1 = $a["price"];
$price2 = $b["price"];
if ($productId1 == $productId2) {
if ($price1 == $price2)
return 0;
else
return ($price1 > $price2) ? 1 : -1;
} else {
return ($productId1 > $productId2) ? 1 : -1;
}
}
?>As you can see, we compare item $a and item $b. If the the two product IDs are the same, we’ll compare prices. To use this is quite easy. You pass an array into the usort method, and watch the magic happen. This is how that works.
<?php
function comparator($a, $b) {
$productId1 = $a["productId"];
$productId2 = $b["productId"];
$price1 = $a["price"];
$price2 = $b["price"];
if ($productId1 == $productId2) {
if ($price1 == $price2)
return 0;
else
return ($price1 > $price2) ? 1 : -1;
} else {
return ($productId1 > $productId2) ? 1 : -1;
}
}
$unsorted = array(
array(
"productId" => 3,
"title" => "Widget #3",
"price" => 6.95,
"discounted" => true
),
array(
"productId" => 4,
"title" => "Widget #4",
"price" => 6.75,
"discounted" => false
),
array(
"productId" => 1,
"title" => "Widget #1",
"price" => 10.95,
"discounted" => false
),
array(
"productId" => 2,
"title" => "Widget #2",
"price" => 11.95
),
array(
"productId" => 3,
"title" => "Widget #3",
"price" => 5.95,
"discounted" => false
)
);
$sorted = $unsorted;
usort($sorted, comparator);
?>Notice how we create a copy of $unsorted as a variable named $sorted first. This is because the usort method works by reference, and will modify the original array. So we need a copy first to preserver the original (unless of course you don’t care about the original).
And that is all! Below is the code sample in full. Cheers, and happy coding!
<?php
function comparator($a, $b) {
$productId1 = $a["productId"];
$productId2 = $b["productId"];
$price1 = $a["price"];
$price2 = $b["price"];
if ($productId1 == $productId2) {
if ($price1 == $price2)
return 0;
else
return ($price1 > $price2) ? 1 : -1;
} else {
return ($productId1 > $productId2) ? 1 : -1;
}
}
$unsorted = array(
array(
"productId" => 3,
"title" => "Widget #3",
"price" => 6.95,
"discounted" => true
),
array(
"productId" => 4,
"title" => "Widget #4",
"price" => 6.75,
"discounted" => false
),
array(
"productId" => 1,
"title" => "Widget #1",
"price" => 10.95,
"discounted" => false
),
array(
"productId" => 2,
"title" => "Widget #2",
"price" => 11.95
),
array(
"productId" => 3,
"title" => "Widget #3",
"price" => 5.95,
"discounted" => false
)
);
$sorted = $unsorted;
usort($sorted, comparator);
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Sorting</title>
</head>
<body>
<h1>Sorting</h1>
<strong>Unsorted:</strong>
<ul>
<?php
foreach ($unsorted as $item) {
printf("<li>%s (%s) - %s</li>\n",
$item["title"],
$item["productId"],
$item["price"]);
}
?>
</ul>
<strong>Sorted:</strong>
<ul>
<?php
foreach ($sorted as $item) {
printf("<li>%s (%s) - %s</li>\n",
$item["title"],
$item["productId"],
$item["price"]);
}
?>
</ul>
</body>
</html>