I cant figure out this array_map issue I am having - php

Question

**EDIT:
I am trying to display the number of keys in my arrays that start with a "P", "M" and "D". I think I should be using array_maps and have some luck with it but I am now stuck and tried looking through the manual, on here and w3schools with no luck.
I'm using version 5.6.36 of PHP with XAMPP on a local server. I've tried playing around with array_maps which I think is the right command to use, but I just cant get my head around how to use it properly. I've read the manual on it, looked on here, looked on youtube and W3Schools with no luck. Can anyone help please?
I have this array:
$tasks = array
(
0 => 'P1',
1 => 'M1',
2 => 'D1',
3 => 'P2',
4 => 'D2'
);
I want it to display this:
Array
(
[P] => 2
[M] => 1
[D] => 2
)
See how it returns the number of P's M's and D's nice and neatly?
From what I understand, the solution code should be something like this:
$array2 = array_map(function(???????){
return ??????????;
}, $tasks);
$array2a = (array_count_values($array2));
echo "<pre>"; print_r($array2a); echo "</pre>";
Please help?!

Answer 1

you can use array_map as following :
$tasks = array
(
0 => 'P1',
1 => 'M1',
2 => 'D1',
3 => 'P2',
4 => 'D2'
);
$charsToCheck = array('P','M','D');
$result = array_map(function($v) use ($charsToCheck){
if(in_array(substr( $v, 0, 1),$charsToCheck))
return substr( $v, 0, 1);
}, $tasks);
print_r(array_count_values($result));
Result:-
Array
(
[P] => 2
[M] => 1
[D] => 2
)

Answer 2

The function array_map() creates one output element from every input element. Since you don't want that, it is the wrong tool. Probably the easiest way to achieve your goal is to use a simple loop. However, if things get more complicated, this may not scale well. For those cases, array_reduce() could come in handy:
$input = [
0 => 'P1',
1 => 'M1',
2 => 'D1',
3 => 'P2',
4 => 'D2',
];
$frequency = array_reduce(
$input,
function ($carry, $item) {
$initial = substr($item, 0, 1);
if (array_key_exists($initial, $carry)) {
$carry[$initial] += 1;
}
return $carry;
},
[
'P' => 0,
'M' => 0,
'D' => 0,
]
);
echo json_encode($frequency, JSON_PRETTY_PRINT) . PHP_EOL;
The point of this is that it defines what to do with a single element ($item) and how to modify the resulting state ($carry) in a single function, keeping this part away from the iteration part. Since this avoids mutable state, this can also be seen as a functional (as in "functional programming") approach.

Answer 3

You cannot use array_map for that... You could use reduce I guess but here's a fast and easy way... Basically you create your new array and do the counting according to the first letter of your tasks array.
$list = new Array();
foreach($tasks as $task){
if($list[$task{0}]){
$list[$task{0}]++;
}else{
$list[$task{0}] = 1;
}
}
The problem you'd get with array_map is that it would always produce a 1:1 ratio of your array, which is not what you want...
(sorry for the bad PHP if it is, been ages...)
EDIT:
Using your edited question, here's your possible usage:
$array2 = array_map(function($val){
return $val{0};
}, $tasks);
The key to both answers is the $var{0} part, this extracts the character at index 0...