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GHC 9.10.3 · lts/ghc-9.10.x · c74966e · 2026-09-27

Modulesort-1.0.0.0Haskell2010

Data.Sort

  • 16 values
  • Packagesort-1.0.0.0
  • Exports16
  • LanguageHaskell2010
  • LicenceBSD-3-Clause
  • SourceOldList.hs

The Vanilla Sorts

3 declarations
valuesort :: Ord a => [a] -> [a]
#

The sort function implements a stable sorting algorithm. It is a special case of sortBy, which allows the programmer to supply their own comparison function.

Elements are arranged from lowest to highest, keeping duplicates in the order they appeared in the input.

The argument must be finite.

Examples
Example1 expression
sort [1,6,4,3,2,5][1,2,3,4,5,6]
Example1 expression
sort "haskell""aehklls"
Example2 expressions
import Data.Semigroup(Arg(..))sort [Arg ":)" 0, Arg ":D" 0, Arg ":)" 1, Arg ":3" 0, Arg ":D" 1][Arg ":)" 0,Arg ":)" 1,Arg ":3" 0,Arg ":D" 0,Arg ":D" 1]
valuesortBy :: (a -> a -> Ordering) -> [a] -> [a]
#

The sortBy function is the non-overloaded version of sort. The argument must be finite.

The supplied comparison relation is supposed to be reflexive and antisymmetric, otherwise, e. g., for _ _ -> GT, the ordered list simply does not exist. The relation is also expected to be transitive: if it is not then sortBy might fail to find an ordered permutation, even if it exists.

Examples
Example1 expression
sortBy (\(a,_) (b,_) -> compare a b) [(2, "world"), (4, "!"), (1, "Hello")][(1,"Hello"),(2,"world"),(4,"!")]
valuesortOn :: Ord b => (a -> b) -> [a] -> [a]
#

Sort a list by comparing the results of a key function applied to each element. sortOn f is equivalent to sortBy (comparing f), but has the performance advantage of only evaluating f once for each element in the input list. This is called the decorate-sort-undecorate paradigm, or Schwartzian transform.

Elements are arranged from lowest to highest, keeping duplicates in the order they appeared in the input.

The argument must be finite.

Examples
Example1 expression
sortOn fst [(2, "world"), (4, "!"), (1, "Hello")][(1,"Hello"),(2,"world"),(4,"!")]
Example1 expression
sortOn length ["jim", "creed", "pam", "michael", "dwight", "kevin"]["jim","pam","creed","kevin","dwight","michael"]
Performance notes

This function minimises the projections performed, by materialising the projections in an intermediate list.

For trivial projections, you should prefer using sortBy with comparing, for example:

Example1 expression
sortBy (comparing fst) [(3, 1), (2, 2), (1, 3)][(1,3),(2,2),(3,1)]

Or, for the exact same API as sortOn, you can use `sortBy . comparing`:

Example1 expression
(sortBy . comparing) fst [(3, 1), (2, 2), (1, 3)][(1,3),(2,2),(3,1)]

Sorting Associations

4 declarations
valuemonoidSortAssocs :: (Monoid a, Ord k) => [(k, a)] -> [(k, a)]
#

Sort the list of associations, aggregating duplicates with the monoid.

valuemonoidSortAssocsBy
  1. :: Monoid a
  2. => k -> k -> Ordering
  3. -> [(k, a)]
  4. -> [(k, a)]
#

Sort the list of associations, aggregating duplicates with the monoid and ordering the keys with the argument compare function.

valuegroupSortAssocs :: Ord k => (k -> a -> [a] -> b) -> [(k, a)] -> [(k, b)]
#

Sort the list of associations, aggregating duplicates with the supplied function.

valuegroupSortAssocsBy
  1. :: k -> k -> Ordering
  2. -> k -> a -> [a] -> b
  3. -> [(k, a)]
  4. -> [(k, b)]
#

Sort the list of associations, aggregating duplicates with the supplied function and ordering the keys with the argument compare function.

Sorting with Monoids

3 declarations
valuemonoidSort :: (Monoid a, Ord a) => [a] -> [a]
#

Sort the list, agregating duplicates with the monoid.

valuemonoidSortOn :: (Monoid a, Ord k) => (a -> k) -> [a] -> [a]
#

Sort the list, agregating duplicates with the monoid and ordering the elements by the items generated by the argument function.

valuemonoidSortBy :: Monoid a => (a -> a -> Ordering) -> [a] -> [a]
#

Sort the list, agregating duplicates with the monoid and ordering the keys with the argument compare function.

Unique Sorts

3 declarations
valueuniqueSort :: Ord a => [a] -> [a]
#

Sort the list, discarding duplicates.

valueuniqueSortOn :: Ord k => (a -> k) -> [a] -> [a]
#

Sort the list, discarding duplicates and ordering the elements by the items generated by the argument function.

valueuniqueSortBy :: (a -> a -> Ordering) -> [a] -> [a]
#

Sort the list, discarding duplicates and ordering the keys with the argument compare function.

Group Sorting

3 declarations
valuegroupSort :: Ord a => (a -> [a] -> b) -> [a] -> [b]
#

Sort a list of elements with a stable sort, grouping together the equal elements with the argument grouping function

valuegroupSortOn :: Ord k => (a -> k) -> (k -> a -> [a] -> b) -> [a] -> [b]
#

Sort a list of elements with a stable sort, using the argument compare function determine the ordering, grouping together the equal elements with the grouping function

valuegroupSortBy :: (a -> a -> Ordering) -> (a -> [a] -> b) -> [a] -> [b]
#

Sort a list of elements with a stable sort, grouping together the equal elements with the argument grouping function.