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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.

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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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