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PHP Arrays and Control Structures

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Sorting Multidimensional Arrays

6:50 with Alena Holligan

Explore sorting multidimensional arrays using a particular inner key element. Dive deeper into sorting and using both array keys and their values to produce the desired results.

TAKE NOTE

When creating an array to use for sorting another array, there are a few things to keep in mind.

  • Array keys MUST be unique.
  • You can sort by either key or value
  • Not all sort functions maintain key association

Loop Options

In PHP, a foreach loop is almost always the fastest, however, you should avoid creating unused variables which not only take up room on a computer, but also in a developers head.

foreach($arr as $key => $notUsed)

is about 50% to 60% faster than using

foreach(array_keys($arr) as $key)

The array_keys function may make it easier to understand what we are actually using from the array.

As another option, if you have additional conditions (such as only needing a certain number) that may keep you from looping through the entire array, it could be useful to use a while loop with the list and each functions to grab your results. 

$newArray=array();
while (count($newArray) < 3 && list($key) = each($list)) {
  $newArray[]=$key;
  ...

It's really up to you, your situation and your team, which option is best. PHP also includes many other array function that may be useful to your situation, such as array_multisort. We'll be learning more about functions, in the PHP Functions Course, but feel free to have some fun exploring array function , adding features and trying multiple ways to accomplish the same task.

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    For our next feature let's add the ability to sort by field. 0:00
    Our filter array will now need to include two values. 0:05
    We still need to store the ID that we used in our list array, but 0:09
    we also need the information we're going to use for sorting. 0:14
    Let's start with priority. 0:18
    instead of allowing PHP to automatically to produce a key for 0:20
    our filter array, we can set our own key value pair. 0:23
    The big thing to remember is that the key must be unique. 0:28
    If you try to use the same key, it will override the existing value. 0:32
    Let's start by adding the item priority as the key of our filter. 0:37
    Then we just want to dump the filter. 0:47
    In the browser, we now see only three items, one from each priority. 0:57
    That is not the result we want, so let's go back and flip our array. 1:03
    The variable key is just a variable, and it doesn't matter what it's called. 1:09
    But let's clear up any confusion, by renaming this, original key. 1:13
    Since the original key was unique from the list array, 1:24
    we can assume that it will continue to be unique. 1:27
    So let's change this to filter originalKey, 1:30
    Equals the item priority. 1:39
    Now when we visit the browser, we can see that our filter array contains 1:46
    all six items, and our list also has six items. 1:51
    However, those items are not unique. 1:55
    Our list is repeating only three unique items. 1:58
    This is because our display loop uses the values of the filter array, 2:02
    and the values are not unique. 2:07
    They're only the priorities, 1, 2, or 3. 2:10
    Let's go back to our display loop. 2:13
    Instead of using the values from the filter array, 2:19
    we want to use the keys of the filter array. 2:23
    A foreach loop can pull either the key value pair, 2:26
    like we did above, or just the value, like we're doing here. 2:30
    You cannot pull the key by itself. 2:35
    Let's change this to pull both the key and the value. 2:38
    ID and value. 2:44
    Then we're just going to ignore the value variable. 2:47
    This time when we refresh the browser, we see all six unique items. 2:52
    But we were already doing this. 2:57
    Now we want to sort. 2:59
    After a filter is created, we want to sort by value, 3:06
    making sure we keep the key association. 3:10
    We do this by using the asort function. 3:16
    We'll add asort($filter) before our dump. 3:19
    Now we can see that our array is sorted by value, and the keys are no longer in 3:28
    ascending order, because they are still attached to the specific priority. 3:32
    This is exactly what we want, so that our items are displayed in order of priority. 3:38
    And as you can see, our list below has our items in order of priority. 3:44
    Now that we can sort by priority, 3:49
    let's update our code to be able to sort by any field we choose. 3:52
    Up near the status variable, let's add a new variable, called field. 3:57
    We'll set this equal to title. 4:04
    Now we're going to add a check, 4:10
    if (isset($field). 4:15
    And we also want to make sure that that item exists. 4:19
    Isset($item[$field]). 4:23
    If so, we can set $filter[$originalKey], 4:32
    = $item[$field], 4:40
    Else, we're going to sort by default our priority. 4:47
    Let's check this out in the browser. 4:54
    Now that the field variable equals title, we see the title in our filter array. 4:57
    And we see that our list is sorted by title. 5:03
    Let's try one more. 5:06
    Let's change the field equal to due. 5:10
    Now when we view the browser, we see things listed by due date. 5:15
    However, our items without a due date are listed first. 5:19
    I want them to be listed last. 5:23
    If we look at our filter array, 5:25
    we can see that the items without a due date are given an integer value. 5:27
    So where is that value coming from? 5:32
    Back in our filter loop, if the item field is not set, we default to priority. 5:35
    We could make our conditional more complicated, but 5:43
    since the priority in our filter array is only used for sorting and 5:46
    not display, we can also simply add 12 to our priority. 5:51
    This will make sure that it will always come after the 12th month, but 5:58
    it will not affect the sort, because every priority will increase by 12. 6:03
    Now we see our empty due dates, after our items with a due date. 6:10
    As an added bonus, these last three items are ordered by priority. 6:15
    Let's clean up our var_dumps and show incomplete tasks ordered by priority. 6:20
    Status is false, and field is priority. 6:35
    Great job! 6:42
    Now we see our incomplete items in order of priority. 6:43
    Awesome! 6:49

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