Portability | portable |
---|---|

Stability | provisional |

Maintainer | libraries@haskell.org |

Safe Haskell | Safe |

An efficient implementation of sets.

These modules are intended to be imported qualified, to avoid name clashes with Prelude functions, e.g.

import Data.Set (Set) import qualified Data.Set as Set

The implementation of `Set`

is based on *size balanced* binary trees (or
trees of *bounded balance*) as described by:

- Stephen Adams, "
*Efficient sets: a balancing act*", Journal of Functional Programming 3(4):553-562, October 1993, http://www.swiss.ai.mit.edu/~adams/BB/. - J. Nievergelt and E.M. Reingold,
"
*Binary search trees of bounded balance*", SIAM journal of computing 2(1), March 1973.

Note that the implementation is *left-biased* -- the elements of a
first argument are always preferred to the second, for example in
`union`

or `insert`

. Of course, left-biasing can only be observed
when equality is an equivalence relation instead of structural
equality.

- data Set a
- (\\) :: Ord a => Set a -> Set a -> Set a
- null :: Set a -> Bool
- size :: Set a -> Int
- member :: Ord a => a -> Set a -> Bool
- notMember :: Ord a => a -> Set a -> Bool
- lookupLT :: Ord a => a -> Set a -> Maybe a
- lookupGT :: Ord a => a -> Set a -> Maybe a
- lookupLE :: Ord a => a -> Set a -> Maybe a
- lookupGE :: Ord a => a -> Set a -> Maybe a
- isSubsetOf :: Ord a => Set a -> Set a -> Bool
- isProperSubsetOf :: Ord a => Set a -> Set a -> Bool
- empty :: Set a
- singleton :: a -> Set a
- insert :: Ord a => a -> Set a -> Set a
- delete :: Ord a => a -> Set a -> Set a
- union :: Ord a => Set a -> Set a -> Set a
- unions :: Ord a => [Set a] -> Set a
- difference :: Ord a => Set a -> Set a -> Set a
- intersection :: Ord a => Set a -> Set a -> Set a
- filter :: (a -> Bool) -> Set a -> Set a
- partition :: (a -> Bool) -> Set a -> (Set a, Set a)
- split :: Ord a => a -> Set a -> (Set a, Set a)
- splitMember :: Ord a => a -> Set a -> (Set a, Bool, Set a)
- map :: (Ord a, Ord b) => (a -> b) -> Set a -> Set b
- mapMonotonic :: (a -> b) -> Set a -> Set b
- foldr :: (a -> b -> b) -> b -> Set a -> b
- foldl :: (a -> b -> a) -> a -> Set b -> a
- foldr' :: (a -> b -> b) -> b -> Set a -> b
- foldl' :: (a -> b -> a) -> a -> Set b -> a
- fold :: (a -> b -> b) -> b -> Set a -> b
- findMin :: Set a -> a
- findMax :: Set a -> a
- deleteMin :: Set a -> Set a
- deleteMax :: Set a -> Set a
- deleteFindMin :: Set a -> (a, Set a)
- deleteFindMax :: Set a -> (a, Set a)
- maxView :: Set a -> Maybe (a, Set a)
- minView :: Set a -> Maybe (a, Set a)
- elems :: Set a -> [a]
- toList :: Set a -> [a]
- fromList :: Ord a => [a] -> Set a
- toAscList :: Set a -> [a]
- toDescList :: Set a -> [a]
- fromAscList :: Eq a => [a] -> Set a
- fromDistinctAscList :: [a] -> Set a
- showTree :: Show a => Set a -> String
- showTreeWith :: Show a => Bool -> Bool -> Set a -> String
- valid :: Ord a => Set a -> Bool

# Strictness properties

This module satisfies the following strictness property:

- Key arguments are evaluated to WHNF

Here are some examples that illustrate the property:

delete undefined s == undefined

# Set type

A set of values `a`

.

# Operators

# Query

lookupLT :: Ord a => a -> Set a -> Maybe aSource

*O(log n)*. Find largest element smaller than the given one.

lookupLT 3 (fromList [3, 5]) == Nothing lookupLT 5 (fromList [3, 5]) == Just 3

lookupGT :: Ord a => a -> Set a -> Maybe aSource

*O(log n)*. Find smallest element greater than the given one.

lookupGT 4 (fromList [3, 5]) == Just 5 lookupGT 5 (fromList [3, 5]) == Nothing

lookupLE :: Ord a => a -> Set a -> Maybe aSource

*O(log n)*. Find largest element smaller or equal to the given one.

lookupLE 2 (fromList [3, 5]) == Nothing lookupLE 4 (fromList [3, 5]) == Just 3 lookupLE 5 (fromList [3, 5]) == Just 5

lookupGE :: Ord a => a -> Set a -> Maybe aSource

*O(log n)*. Find smallest element greater or equal to the given one.

lookupGE 3 (fromList [3, 5]) == Just 3 lookupGE 4 (fromList [3, 5]) == Just 5 lookupGE 6 (fromList [3, 5]) == Nothing

isSubsetOf :: Ord a => Set a -> Set a -> BoolSource

*O(n+m)*. Is this a subset?
`(s1 `

tells whether `isSubsetOf`

s2)`s1`

is a subset of `s2`

.

isProperSubsetOf :: Ord a => Set a -> Set a -> BoolSource

*O(n+m)*. Is this a proper subset? (ie. a subset but not equal).

# Construction

insert :: Ord a => a -> Set a -> Set aSource

*O(log n)*. Insert an element in a set.
If the set already contains an element equal to the given value,
it is replaced with the new value.

# Combine

union :: Ord a => Set a -> Set a -> Set aSource

*O(n+m)*. The union of two sets, preferring the first set when
equal elements are encountered.
The implementation uses the efficient *hedge-union* algorithm.
Hedge-union is more efficient on (bigset `union`

smallset).

difference :: Ord a => Set a -> Set a -> Set aSource

*O(n+m)*. Difference of two sets.
The implementation uses an efficient *hedge* algorithm comparable with *hedge-union*.

intersection :: Ord a => Set a -> Set a -> Set aSource

*O(n+m)*. The intersection of two sets.
Elements of the result come from the first set, so for example

import qualified Data.Set as S data AB = A | B deriving Show instance Ord AB where compare _ _ = EQ instance Eq AB where _ == _ = True main = print (S.singleton A `S.intersection` S.singleton B, S.singleton B `S.intersection` S.singleton A)

prints `(fromList [A],fromList [B])`

.

# Filter

partition :: (a -> Bool) -> Set a -> (Set a, Set a)Source

*O(n)*. Partition the set into two sets, one with all elements that satisfy
the predicate and one with all elements that don't satisfy the predicate.
See also `split`

.

split :: Ord a => a -> Set a -> (Set a, Set a)Source

*O(log n)*. The expression (

) is a pair `split`

x set`(set1,set2)`

where `set1`

comprises the elements of `set`

less than `x`

and `set2`

comprises the elements of `set`

greater than `x`

.

splitMember :: Ord a => a -> Set a -> (Set a, Bool, Set a)Source

*O(log n)*. Performs a `split`

but also returns whether the pivot
element was found in the original set.

# Map

map :: (Ord a, Ord b) => (a -> b) -> Set a -> Set bSource

*O(n*log n)*.

is the set obtained by applying `map`

f s`f`

to each element of `s`

.

It's worth noting that the size of the result may be smaller if,
for some `(x,y)`

, `x /= y && f x == f y`

mapMonotonic :: (a -> b) -> Set a -> Set bSource

*O(n)*. The

, but works only when `mapMonotonic`

f s == `map`

f s`f`

is monotonic.
*The precondition is not checked.*
Semi-formally, we have:

and [x < y ==> f x < f y | x <- ls, y <- ls] ==> mapMonotonic f s == map f s where ls = toList s

# Folds

## Strict folds

foldr' :: (a -> b -> b) -> b -> Set a -> bSource

*O(n)*. A strict version of `foldr`

. Each application of the operator is
evaluated before using the result in the next application. This
function is strict in the starting value.

foldl' :: (a -> b -> a) -> a -> Set b -> aSource

*O(n)*. A strict version of `foldl`

. Each application of the operator is
evaluated before using the result in the next application. This
function is strict in the starting value.

## Legacy folds

fold :: (a -> b -> b) -> b -> Set a -> bSource

*O(n)*. Fold the elements in the set using the given right-associative
binary operator. This function is an equivalent of `foldr`

and is present
for compatibility only.

*Please note that fold will be deprecated in the future and removed.*

# Min/Max

deleteFindMin :: Set a -> (a, Set a)Source

*O(log n)*. Delete and find the minimal element.

deleteFindMin set = (findMin set, deleteMin set)

deleteFindMax :: Set a -> (a, Set a)Source

*O(log n)*. Delete and find the maximal element.

deleteFindMax set = (findMax set, deleteMax set)

maxView :: Set a -> Maybe (a, Set a)Source

*O(log n)*. Retrieves the maximal key of the set, and the set
stripped of that element, or `Nothing`

if passed an empty set.

minView :: Set a -> Maybe (a, Set a)Source

*O(log n)*. Retrieves the minimal key of the set, and the set
stripped of that element, or `Nothing`

if passed an empty set.

# Conversion

## List

*O(n)*. An alias of `toAscList`

. The elements of a set in ascending order.
Subject to list fusion.

## Ordered list

toAscList :: Set a -> [a]Source

*O(n)*. Convert the set to an ascending list of elements. Subject to list fusion.

toDescList :: Set a -> [a]Source

*O(n)*. Convert the set to a descending list of elements. Subject to list
fusion.

fromAscList :: Eq a => [a] -> Set aSource

*O(n)*. Build a set from an ascending list in linear time.
*The precondition (input list is ascending) is not checked.*

fromDistinctAscList :: [a] -> Set aSource

*O(n)*. Build a set from an ascending list of distinct elements in linear time.
*The precondition (input list is strictly ascending) is not checked.*

# Debugging

showTree :: Show a => Set a -> StringSource

*O(n)*. Show the tree that implements the set. The tree is shown
in a compressed, hanging format.

showTreeWith :: Show a => Bool -> Bool -> Set a -> StringSource

*O(n)*. The expression (`showTreeWith hang wide map`

) shows
the tree that implements the set. If `hang`

is
`True`

, a *hanging* tree is shown otherwise a rotated tree is shown. If
`wide`

is `True`

, an extra wide version is shown.

Set> putStrLn $ showTreeWith True False $ fromDistinctAscList [1..5] 4 +--2 | +--1 | +--3 +--5 Set> putStrLn $ showTreeWith True True $ fromDistinctAscList [1..5] 4 | +--2 | | | +--1 | | | +--3 | +--5 Set> putStrLn $ showTreeWith False True $ fromDistinctAscList [1..5] +--5 | 4 | | +--3 | | +--2 | +--1