Counting items in each category of a multidimensional array - php

Question

I have a multidimensional array and I need to count how many items are in each category:
array (
array(
'name' => 'Bob',
'category' => '2'
),
array(
'name' => 'Bill',
'category' => '6'
),
array(
'name' => 'John',
'category' => '1'
),
array(
'name' => 'Jack',
'category' => '2'
),
)
I want to be able to split these up into categories.
For example;
Category 2 contains 2 items
Category 1 contains 1 item
Category 6 contains 1 item
Just to get the count of each category would be great, but to be able to re-arrange the array into categories would also be useful. I'd like to be able to do both.
I've tried searching StackOverflow but I couldn't find this specific query. I'm guessing this may use array_map somewhere but I'm not good with that function.
Any help is greatly appreciated!

Answer 1

If your array isn't too big a straightforward approach might be the easiest one. Create a new array, use categories as keys and iterate over your array, counting items.

Answer 2

I have written 3 functions that solves the criteria you have described. Keep in mind these functions are bare minimum and lack error handling. It is also assumed the $categories array which all the functions requires has the structure outlined in your question.
The first rearranges all items into the correct category.
function rearrangeCategories(array $categories) {
$calculated = [];
foreach($categories as $category) {
$calculated[$category['category']][] = $category['name'];
}
return $calculated;
}
The second creates an associative array of the amount of items in each category. The array index is the category name/id and the value is an integer declaring the amount of items.
function categoriesCount(array $categories) {
$calculated = [];
$arranged = rearrangeCategories($categories);
foreach($arranged as $category => $values) {
$calculated[$category] = count($values);
}
return $calculated;
}
The third function checks how many items are stored inside a specific category. If the category doesn't exists FALSE is returned. Otherwise an integer is returned.
function categoriesItemCount(array $categories, $key) {
$arranged = rearrangeCategories($categories);
if(!array_key_exists($key, $arranged)) {
return false;
}
return count($arranged[$key]);
}
I hope this helps, happy coding.

Answer 3

You can use something like this
$arr =
array (
array(
'name' => 'Bob',
'category' => '2'
),
array(
'name' => 'Bill',
'category' => '6'
),
array(
'name' => 'John',
'category' => '1'
),
array(
'name' => 'Jack',
'category' => '2'
),
);
$categoryCount = array();
$categoryList = array();
array_map(function($a) use (&$categoryCount, &$categoryList) {
$categoryId = $a['category'];
if (!isset($categoryCount[$categoryId])) {
$categoryCount[$categoryId] = 0;
}
$categoryCount[$categoryId]++;
if (!isset($categoryList[$categoryId])) {
$categoryList[$categoryId] = array();
}
$categoryList[$categoryId][] = $a['name'];
}, $arr);
print_r($categoryCount);
print_r($categoryList);
This will create 2 arrays: one with the counts and one with the elements rearranged

Answer 4

Try this way, i think it will fulfill your requirements.
$arr=array (
array(
'name' => 'Bob',
'category' => '2'
),
array(
'name' => 'Bill',
'category' => '6'
),
array(
'name' => 'John',
'category' => '1'
),
array(
'name' => 'Jack',
'category' => '2'
),
);
$result = call_user_func_array('array_merge_recursive', $arr);
//for just show array
print '<pre>';
print_r(array_count_values($result['category']));
print '</pre>';
//loop as you need
foreach(array_count_values($result['category']) as $k=>$v){
$item=($v>1)? 'items':'item';
echo "Category ".$k." Contains " .$v." ".$item."<br/>";
}