mashhadi
I have an list which is like
[[1, 5], [3, 12], [4, 10]]
i want to change it to a map like below
%{
1 => 5,
3 => 12,
4 => 10
}
Currently i am using following code and my question is , is there a better way to do. i mean if there is more concise way, or may be a built-in function to do so.
Enum.reduce([[1, 5], [3, 12], [4, 10]],%{}, fn row, acc ->
acc
|> Map.put(List.first(row), List.last(row))
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dimitarvp
I would not use
Map.putorEnum.intobecause that means that the runtime copies the map, adds one more pair to it, then throws out the previous one – N times. That’s very inefficient.Go with what @NobbZ suggested: it basically says “construct a new map using this list and then use this function (the second parameter, in this case
List.to_tuple) to convert each element of the list to a key/value tuple” – which is the format thatMap.newexpects.For (supposedly) even bigger efficiency I’d write this:
This has the added benefit that it will break if your list is malformed, namely you want a list of sublists and each of the sublists must be exactly 2 elements long. If there’s even one sublist that is not 2-sized then you’ll get a runtime error. Annoying, sure, but you’ll know you have a bug very quickly and can fix it.
Also Liked
NobbZ
It’s quite uncommon to use a list of lists like this, a more common approach would be to have the list as a list of binary tuples.
So if you have control over the shape of the incoming list, make it
[{1, 2}, {3, 4}], then it’s easy as callingMap.new(list).Having said that, you can also use
Map.new/2andList.to_tuple/1as this with your initial list shape:Map.new(list, &List.to_tuple/1).fuelen
kokolegorille
While Enum.into is the simplest, You could have rewritten your Enum.reduce like this.