[Haskell-beginners] Python's collections.defaultdict(list) in Haskell?

[Sylvain Henry]

import qualified Data.Map as Map

-- if your keys are unique
let xs = [("Item0", ["a","b","c"]), ("Item1", ["x","y"]), ("Item2",
["abc","def"])]
Map.fromList xs

-- if you want to combine values for keys that are equal
let xs = [("Item0", ["a","b","c"]), ("Item1", ["x","y"]), ("Item0",
["abc","def"])]
Map.fromListWith (++) xs

--
Sylvain


2015-11-10 3:07 GMT+01:00 Dan Stromberg <strombrg at gmail.com>:

>
> I'm spending a little time here and there to learn some Haskell.  I'm
> coming from a chiefly Python/C/bash background.
>
> I want to build a Data.Map where the keys are strings, and the values are
> lists of strings.
>
> In Python, collections.defaultdict(list) makes this pretty
> straightforward. It gives a hash table ("dict") that has values that
> default to an empty list, since list() produces an empty list. More info
> here:
> https://docs.python.org/3/library/collections.html#collections.defaultdict
>
> Is there an equivalent in Haskell?
>
> Thanks!
>
> --
> Dan Stromberg
>
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>
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