map-exts: Extensions for Data.Map

This is a package candidate release! Here you can preview how this package release will appear once published to the main package index (which can be accomplished via the 'maintain' link below). Please note that once a package has been published to the main package index it cannot be undone! Please consult the package uploading documentation for more information.


Please see

[Skip to ReadMe]


Change logNone available
Dependenciesbase (>=4.7 && <5), bytestring, cassava, containers [details]
Copyright2016 Elsen, Inc
AuthorCharles Cooper
CategoryData Structures
Home page
Executablestitanic-example, example
UploadedThu Apr 14 21:45:51 UTC 2016 by coopercm




Maintainers' corner

For package maintainers and hackage trustees

Readme for map-exts-

[back to package description]


This module contains some extensions to Data.Map. Some of them are convenience functions.

It also contains functions to support a split-apply-combine workflow, by representing labeled, multi-dimensional data as multiply nested Maps. For instance, a two dimensional matrix with one axis indexed by 'Name's and the other axis labeled by 'Job's, we would represent such a structure with a Lookup2 Name Job Double. Such a structure is not terribly efficient (it takes O(n log(n)) space and O(log(n)) time for insert/update/delete operations with high constant factor owing to all the pointer manipulation), but it is expressive.

split : groupMapBy apply : fmap combine : foldr/foldMap reshape : transpose

Say we had a dataFrame :: (Lookup2 Name Job Age). We could group by Job by running transpose on it. If we wanted to find the average Age in a job, we could define

mean :: Map k v -> Int
mean xs = foldr (+) 0 xs / Map.size xs

type Name = String
type Job  = String
type Age  = Double
averageAgeInJob :: Lookup2 Name Job Age -> Map Job Age
averageAgeInJob dataFrame = fmap mean $ transpose dataFrame

This illustrates applying an aggregation over a particular index by reshaping with transpose, defining a fold, and then focusing it inside the structure using fmap.