[Haskell-cafe] Data.Map: Values to keys and keys to values

Johan Tibell johan.tibell at gmail.com
Thu Jun 16 15:38:02 CEST 2011

On Thu, Jun 16, 2011 at 3:01 PM, Dmitri O.Kondratiev <dokondr at gmail.com> wrote:
> Hi,
> Data.Map has many great functions, yet I could not find the one that allows
> from one map create another map where keys are values and values are keys of
> the first one.
> Something like:
> transMap:: (Ord k, Ord a) => Map k a -> Map a k

I don't think implementing this function in the library would add much
as it cannot be implemented more efficiently with access to the
internal representation than it can using the public API. Just write

    transMap = M.fromList . map swap . M.toList

and stick it in some utility file.


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