Clojure's partition-by in PHP? - php

Question

coming from an FP background and now learning PHP I'm naturally missing some beloved higher-order functions. I was wondering if there's anything like Clojure's partition-by in PHP. Here's the official description of what it does:
(partition-by f)(partition-by f coll)
Applies f [a function] to each value in coll, splitting it each time f
returns a new value. Returns a lazy seq of partitions. Returns a
stateful transducer when no collection is provided.
I don't really care about the lazy and transducer parts (which I guess are out of the question in PHP anyway, am I right?) What I need to do is tranform an array like this :
[["year" => 2019, "val" => "foo"],
["year" => 2019, "val" => "bar"],
["year" => 2020, "val" => "baz"],
["year" => 2020, "val" => "boo)"]]
into this:
[[["year" => 2019, "val" => "foo"],
["year" => 2019, "val" => "bar"]],
[["year" => 2020, "val" => "baz"],
["year" => 2020, "val" => "boo)"]]]
i.e. I want to group them by the result of a function like this:
function getYear($pair)
{
return $pair["year"];
}
I haven't tried yet to code something like this up myself, but I was wondering if anything like this exists in a functional lib (or even the core?) of PHP.

Answer 1

I don't think this exists as a language feature. At least I haven't or couldn't find anything.
However, (unless I misunderstood) this should give you the result you described, with the caveat that the initial array must first be sorted by the partition value:
$f = [
["year" => 2019, "val" => "foo"],
["year" => 2019, "val" => "bar"],
["year" => 2020, "val" => "baz"],
["year" => 2020, "val" => "boo)"]
];
var_dump(partitionMultidim($f, "year"));
function partitionMultidim(array $values, string $key):array{
$new = [];
$p = $values[0][$key]; // alternatively check if exists in loop and set if not
$partitionNum = 0;
foreach($values as $value){
// what is the current value?
$curPartitionVal = $value[$key]; // or getYear($b);
// has the value changed?
if ( $p !== $curPartitionVal ){
// set the next partition value
$p = $curPartitionVal;
// new partition index
$partitionNum++;
}
// add to the new array
$new[$partitionNum][] = $value;
}
return $new;
}

Answer 2

This does not exist as a language feature. However, there are ready classes that do the same. Example:
$f = [
["year" => 2020, "val" => "baz"],
["year" => 2019, "val" => "foo"],
["year" => 2019, "val" => "bar"],
["year" => 2020, "val" => "boo)"]
];
//https://github.com/jspit-de/tableArray
$newArr = tableArray::create($f)
->orderBy('year ASC,val ASC')
->fetchGroup(['year'])
;
//test output
echo '<pre>';
var_dump($newArr);
Output:
array(2) {
[2019]=>
array(2) {
[0]=>
array(2) {
["year"]=>
int(2019)
["val"]=>
string(3) "foo"
}
[1]=>
array(2) {
["year"]=>
int(2019)
["val"]=>
string(3) "bar"
}
}
[2020]=>
array(2) {
[2]=>
array(2) {
["year"]=>
int(2020)
["val"]=>
string(4) "boo)"
}
[3]=>
array(2) {
["year"]=>
int(2020)
["val"]=>
string(3) "baz"
}
}
}