PHP Array needs fixed (consolidated/merged) - php

Question

I have this multidimensional array which I'll name "original":
$original=
array
0 =>
array
'animal' => 'cats'
'quantity' => 1
1 =>
array
'animal' => 'dogs'
'quantity' => '1'
2 =>
array
'animal' => 'cats'
'quantity' => '3'
However, I want to merge internal arrays with the same animal to produce this new array (with quantities combined):
$new=
array
0 =>
array
'animal' => 'cats'
'quantity' => 4
1 =>
array
'animal' => 'dogs'
'quantity' => '1'
I understand that there are similar questions on stackoverflow, but not similar enough for me to be able to figure out how to use the feedback those questions have gotted to apply to this specific example. Yes, I know I probably look stupid to a lot of you, but please remember that there was a time when you too didn't know crap about working with arrays :)
I've tried the following code, but get Fatal error: Unsupported operand types (Referring to line 11). And if I got that error to go away, I'm not sure if this code would even produce what I'm trying to achieve.
$new = array();
foreach($original as $entity){
if(!isset($new[$entity["animal"]])){
$new[$entity["animal"]] = array(
"animal" => $entity["animal"],
"quantity" => 0,
);
}
$new[$entity["animal"]] += $entity["quantity"];
}
So, I don't know what I'm doing and I could really use some help from the experts.
To try to give a super clear question, here goes... What changes do I need to make to the code so that it will take $original and turn it into $new? If the code I provided is totally wrong, could you provide an alternative example that would do the trick? Also, the only language I am familiar with is PHP, so please provide an example using only PHP.
Thank you

Answer 1

You're very close.
$new[$entity["animal"]] += $entity["quantity"];
needs to be
$new[$entity["animal"]]['quantity'] += $entity["quantity"];
In your if ( !isset [...] ) line, you're setting $new[$entity['animal']] to an array, so you need to access the 'quantity' field of that array before trying to add the new quantity value to it.

Answer 2

One of the reasons why your code is not working is that you're using the animal name as the array index, not the integer index which is used in your desired output.
Try this:
$new = array(); // Desired output
$map = array(); // Map animal names to index in $new
$idx = 0; // What is the next index we can use
foreach ($original as $entity) {
$animal = $entity['animal'];
// If we haven't saved the animal yet, put it in the $map and $new array
if(!isset($map[$animal])) {
$map[$animal] = $idx++;
$new[$map[$animal]] = $entity;
}
else {
$new[$map[$animal]]['quantity'] += $entity['quantity'];
}
}

Answer 3

This works:
$new = array();
$seen = array();
foreach($original as $entity) {
// If this is the first time we're encountering the animal
if (!in_array($entity['animal'], $seen)) {
$new[] = $entity;
$seen[] = $entity['animal'];
// Otherwise, if this animal is already in the new array...
} else {
// Find the index of the animal in the new array...
foreach($new as $index => $new_entity) {
if ($new_entity['animal'] == $entity['animal']) {
// Add to the quantity
$new[$index]['quantity'] += $entity['quantity'];
}
}
}
}
Your example was using the animal name as the index, yet the actual index is just an integer.
However, I think the resulting array would be easier to use and easier to read if it was formatting like this instead:
array('cats' => 4, 'dogs' => 1)
That would require different but simpler code than above... but, it wouldn't be a direct response to your question.