Function to build associative arrays from an input list and two user functions producing keys and values for the output list

[gvlasov]

This is a feature request. Something like this:

create_map(
  ['cat', 'bear', 'aardvark'],
  function($element, $index, $collection) {
    return strlen($element);
  }
);
/*
returns [
  'cat'=>3,
  'bear'=>4,
  'aardvark'=>8
];
*/

I'm not sure what that function would be called, I admit that it should have a better name than create_map

Couldn't properly explain what I want in the original post, see a comment below: https://github.com/lstrojny/functional-php/issues/164#issuecomment-402945532

[phanan]

create_assoc? Anw, what might be a use case for this?

[gvlasov]

@phanan Sorry, I messed up explaining what I want.

Basically what I suggest is an analogue to Yii2's ArrayHelpers::map. It doesn't do what map does in functional programming (i.e. taking a list and returning another list), but rather it takes:

• an input list
• a function to produce keys of the output list
• a function to produce values of the output list

and creates an associative array (a map) from the keys to values for the same elements of the original array, e.g.:

ArrayMap::map(
  [
    ['id' => 1, 'name' => 'Bob'],
    ['id' => 2, 'name' => 'Joj'],
    ['id' => 3, 'name' => 'Yoy'], 
  ],
  function($elem, $index) {
    return $elem['id'];
  },
  function($elem, $index) {
    return 'Mister '.$elem['name'];
  }
);
/*
returns
[
 1 => 'Mister Bob',
 2 => 'Mister Joj',
 3 => 'Mister Yoy'
]
*/

Example: I have a list of books. I need to get a map from book ids to their names to pass to a view to render a <select> element

In plain PHP:

$ids2Names = [];
foreach ($books as $book) {
  $ids2Names[$book->id] = $book->name;
}

With ArrayHelper::map from Yii2:

ArrayHelper::map(
  $books,
  function($book) { return $book->id; },
  function($book) { return $book->name; }
);

With create_assoc:

create_assoc(
  $books,
  function($book) { return $book->id; },
  function($book) { return $book->name; }
);

Benefit of this approach in comparison to plain php is that it is more semantical and isolates logic for getting keys and values, doesn't require you to come up with the assotiative array name. We can also add a check that no two entries of the input array produce the same key.

[gvlasov]

@phanan Also create_asoc can be useful for print debugging in some cases. But most importantly it can be useful in formatting input data in an MVC view.

[lstrojny]

array_combine(map(…, …), map(…, …)) is not good enough?

[gvlasov]

@lstrojny

array_combine(
  map($books, function($book) {
    return $book->id;
  }),
  map($books, function($book) {
      return $book->name;
  })
);

vs

create_assoc(
  $books,
  function($book) { return $book->id; },
  function($book) { return $book->name; }
);

Also if we want to do something like this:

create_assoc(
  filter(
    $bookRepository->getBooks(),
    function() {
       // maybe some more logic
    }
  ),

  function($book) { return $book->id; },
  function($book) { return $book->name; }
);

then in the array_combine() case we'll have to use an extra variable.

Also map and the input array are not written twice in create_assoc. Also using create_assoc would explicitly state the relation between keys and values, unlike array_combine where you'd have to parse it visually. I think functional-php has many functions that are much more niche than this one, and ability to create associative arrays easily to me seems to be an essential but missing piece of this library ($preserveKeys everywhere).

[phanan]

Personally, I don't see a big gain :/ Btw, your create_assoc's example should have been written this way for a fairer comparison:

create_assoc(
  $books,
  function($book) { 
    return $book->id; 
  },
  function($book) {
    return $book->name; 
  }
);

As you can see, create_assoc is one LoC longer ;)

[gvlasov]

@phanan It is not about LoC, it is about the amount of nested expressions ;;;)))

Btw, if you rewrite my create_assoc example, then consider doing the same for array_combine:

array_combine(
  map(
    $books,
    function($book) {
      return $book->id;
    }
  ),
  map(
    $books,
    function($book) {
      return $book->name;
    }
  )
);

[gvlasov]

Ok, let's wait several months till the few people who haven't already searched for a less verbose way to build associative arrays in PHP start upvoting this coming via Google, if you don't think this suggestion is useful.

[lstrojny]

Another option that came to mind was to use reindex:

map(
    function ($book) { return $book->name; },
    reindex(
        function($book) { return $book->id; },
        filter($collection, …)
    )
)

But I like that the create_assoc reads so well. Let me ponder this a bit longer

[tzkmx]

What do you think about unfold? https://github.com/apantle/fun-php/blob/master/README.md#unfold

It does already what you are looking for, if the passed function is unary is called with just the input as argument, and allows optional values or even a helper to pass around values between applied functions.

We use it to apply a bunch of different service calls to a single entry, like a tap but calling many functions to build a single assoc array.

Happy to merge this little function of mine with more tests and a better suited name to the project.

[tzkmx]

So @gvlasov, my proposal it very similar to what you have requested, but instead of directly building the associative array, instead I'm returning a function that allow to build any number of associative arrays, based on the same set of rules with a single or a series of input values.

If there are some issues on my proposal, please let me know to make it more useful. My tests are copied from the independent project I've worked this function, and they are thought more closely to a complement of another library that I use to map associative arrays, reducing them being a common case. This function makes the opposite, that's why in the little collection I've built I called it originally unfold.

[drupol]

Hi,

Is this what you're looking for?