PHP array: Conditional sum - php

Question

I have a an array looking like this:
$array = array("a1" => 0, "a2" => 2, "a3" => 1, "b1" => 2, "b2" => 3);
I would like to sum values foreach "unique" key when only the first character is considered. The result should then be:
$newarray = array("a" => 3, "b" => 5);
I have tried using a foreach() loop within another foreach() loop like this:
foreach ($xml->children() as $output) {
foreach ($array as $key => $value) {
if (substr($key,0,1) == $output->KEY) {
$sum += $value; echo $sum;
}
}
}
It didn't work as the results apparently added the prior calculations.

Answer 1

Simple solution:
$final_array=[];
foreach($array as $key=>$value){
$final_array[$key[0]] = (isset($final_array[$key[0]])) ? $final_array[$key[0]]+$value : $value;
}
print_r($final_array);
Output:- https://3v4l.org/tZ4Ei

Answer 2

You can try this one. It will take first letter from your key and make sum of all values with that first letter keys.
<?php
$sum = [];
foreach ($array as $key => $value) {
$letter = substr($key,0,1);
if (!isset($sum[$letter])){$sum[$letter] = 0;}
$sum[$letter] += $value;
}
var_dump($sum);

Answer 3

A simple isset should do it:
$array = array("a1" => 0, "a2" => 2, "a3" => 1, "b1" => 2, "b2" => 3);
$result = array();
foreach ($array as $oldkey => $val) {
$newkey = substr($oldkey, 0, 1);
if (isset($result[$newkey]) === false)
$result[$newkey] = $val;
else
$result[$newkey] += $val;
}
var_dump($result);

Answer 4

Try this way
$array = array('a1' => 0, 'a2' => 2, 'a3' => 3, 'b1' => 2, 'b2' => 3);
$result = array();
foreach($array as $key => $value){
if(isset($result[$key[0]])){
$result[$key[0]] = $result[$key[0]]+$value;
} else {
$result[$key[0]] = $value;
}
}
print_r($result);

Answer 5

Quick and Easy, you can have any number of numbers in the array after the characters.
<?php
$array = ["a1" => 0, "a2" => 2, "a3" => 1, "b1" => 2, "b2" => 3];
$newArray = [];
foreach ($array as $key => $value) {
$key = preg_replace("/[0-9]*$/", "", $key);
$newArray[$key] = (isset($newArray[$key])) ? $newArray[$key] + $value : $value;
}
print_r($newArray);