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In the last video we used the built-in
PHP function, array_rand,

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to pull four random keys to use for our
suggestions, displayed on the homepage.

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For each of our categories,
books, movies, and

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music, we want to display just the items
in that corresponding category.

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To do this,

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we'll create our own function that works
much like the array_rand function.

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We'll pass in two parameters and
return an array of keys.

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While currently,
we only want to pull the category keys for

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the catalog page, we may decide to use
that for something else in the future.

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Let's go ahead and

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add that to our functions.php
file in our includes directory.

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Then we can simply include
the functions file

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if we want to use that function later.

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Let's get coding.

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Let's go back into functions.php.

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We're going to add a second
function called array_category.

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For the parameters, we need the catalog
array, And the category we wish to return.

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We want to return an array.

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So let's start by creating an empty
array variable named output.

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And we'll return output.

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We need to loop through our catalog array,
so once again we create a foreach loop.

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foreach ($catalog as

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$id => $item).

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For each item,

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we need to check if the category is the
one that matches our category parameter.

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If ($category ==, because we're comparing,

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$item["category"]).

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If you look at the data.php file,

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you'll see that the values for
the category are capitalized.

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But we don't really need
this to be case sensitive.

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So we're going to use
another built-in function and

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convert both of these
string values to lowercase.

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The function is strtolower.

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We simply pass the string
value we want to convert, and

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it returns the string
converted to lowercase.

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We add this to both our variables, and

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now the capitalization of
the category we pass in won't matter.

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And how we've stored our
variable won't matter.

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We are looking only at
the letters themselves.

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If the category we passed in,
matches the category of the current

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item we are looping through,
we need to add the id to the output array.

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$output[] = $id;.

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Our function is ready, we just need
to call it from our catalog page.

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Let's go into our index.php file, and

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copy our call to our function,
as well as our foreach loop.

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Then we'll go into catalog and
replace our foreach loop.

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Now let's change these values a little.

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Instead of random, we're going
to be calling our category ids.

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So let's call this $categories.

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Next, we want to call our
new function array_category.

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We'll still pass the catalog variable but
for the second parameter,

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we need to pass the category.

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At the top of this page,
we already set the section variable.

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Here, here, here, or here.

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So let's use that.

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Now when we preview our site and
click on books, we see just the books.

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When we click on movies,
we see just our movie items.

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And when we click on music,
we see just our music items.

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That looks great, but what happens when
we wanna try to view the full catalog?

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We don't see anything at all.

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That's not what we want.

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What we want is it to show all the items
in our catalog on the full catalog page.

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Let's take a look at our code.

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On the catalog page, we're passing
the category of books, movies, or music.

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If we haven't chosen one of these,

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we're passing the default
of section which is null.

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So we need to update our
function to return all keys

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if null is passed as the category.

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In functions.php,
let's modify our function.

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At the top of the function,
let's do a simple check.

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If ($category == null)

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we're going to return

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array_keys($catalog).

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You guessed it,
it returns an array of just the keys.

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Now when we go back to our browser and
refresh the page,

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we see all of our items
on our full catalog page.

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Our site is finally starting
to look like a real library.

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You're doing great.

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You've learned a lot about arrays and
functions.

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There's just one more thing I think would
be really helpful before moving on,

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sorting.