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GHC 9.14.1 · lts/ghc-9.14.x · b922848 · 2026-10-12

Moduleutility-ht-0.0.17.2Haskell98

Data.List.Key

Variant of Data.List functions like group, sort where the comparison is performed on a key computed from the list elements. In principle these functions could be replaced by e.g. sortBy (compare on f), but f will be re-computed for every comparison. If the evaluation of f is expensive, our functions are better, since they buffer the results of f.

Synopsis
valuenub :: Eq b => (a -> b) -> [a] -> [a]
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valuesort :: Ord b => (a -> b) -> [a] -> [a]
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valuegroup :: Eq b => (a -> b) -> [a] -> [[a]]

Divides a list into sublists such that the members in a sublist share the same key. It uses semantics of groupBy, not that of groupBy.

valuemerge :: Ord b => (a -> b) -> [a] -> [a] -> [a]
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