Data.StringMap.Lazy

An efficient implementation of maps from strings to arbitrary values.

Values can associated with an arbitrary byte key. Searching for keys is very fast, but the prefix tree probably consumes more memory than Data.Map. The main differences are the special prefixFind functions, which can be used to perform prefix queries. The interface is heavily borrowed from Data.Map and Data.IntMap.

Most other function names clash with Prelude names, therefore this module is usually imported qualified, e.g.

 import Data.StringMap (StringMap)
 import qualified Data.StringMap as T

Many functions have a worst-case complexity of O(min(n,L)). This means that the operation can become linear with the number of elements with a maximum of L, the length of the key (the number of bytes in the list). The functions for searching a prefix have a worst-case complexity of O(max(L,R)). This means that the operation can become linear with R, the number of elements found for the prefix, with a minimum of L.

The module exports include the internal data types, their constructors and access functions for ultimate flexibility. Derived modules should not export these (as shown in Holumbus.Data.StrMap) to provide only a restricted interface.

Map type

data StringMap v

Instances

Functor StringMap

Typeable1 StringMap

Foldable StringMap

Traversable StringMap

Eq v => Eq (StringMap v)

Ord v => Ord (StringMap v)

Read a => Read (StringMap a)

Show v => Show (StringMap v)

Binary a => Binary (StringMap a)

NFData a => NFData (StringMap a)

type Key = [Sym]

Operators

(!) :: StringMap a -> Key -> a

O(min(n,L)) Find the value at a key. Calls error when the element can not be found.

Query

value :: Monad m => StringMap a -> m a

O(1) Extract the value of a node (if there is one)

valueWithDefault :: a -> StringMap a -> a

O(1) Extract the value of a node or return a default value if no value exists.

null :: StringMap a -> Bool

O(1) Is the map empty?

size :: StringMap a -> Int

O(n) The number of elements.

member :: Key -> StringMap a -> Bool

O(min(n,L)) Is the key a member of the map?

lookup :: Monad m => Key -> StringMap a -> m a

O(min(n,L)) Find the value associated with a key. The function will return the result in the monad or fail in it if the key isn't in the map.

findWithDefault :: a -> Key -> StringMap a -> a

O(min(n,L)) Find the value associated with a key. The function will return the result in the monad or fail in it if the key isn't in the map.

prefixFind :: Key -> StringMap a -> [a]

O(max(L,R)) Find all values where the string is a prefix of the key.

prefixFindWithKey :: Key -> StringMap a -> [(Key, a)]

Deprecated: use toList . prefixFilter instead

O(max(L,R)) Find all values where the string is a prefix of the key and include the keys in the result.

prefixFindWithKeyBF :: Key -> StringMap a -> [(Key, a)]

Deprecated: use toListShortestFirst . prefixFilter instead

O(max(L,R)) Find all values where the string is a prefix of the key and include the keys in the result. The result list contains short words first

lookupRange :: Key -> Key -> StringMap a -> StringMap a

Combination of lookupLE and lookupGE

 keys $ lookupRange "a" "b" $ fromList $ zip ["", "a", "ab", "b", "ba", "c"] [1..] = ["a","ab","b"]

For all keys in k = keys $ lookupRange lb ub m, this property holts true: k >= ub && k <= lb

Construction

empty :: StringMap v

Creates an empty string map

 null $ empty == True

singleton :: Key -> a -> StringMap a

O(1) Create a map with a single element.

Insertion

insert :: Key -> a -> StringMap a -> StringMap a

O(min(n,L)) Insert a new key and value into the map. If the key is already present in the map, the associated value will be replaced with the new value.

insertWith :: (a -> a -> a) -> Key -> a -> StringMap a -> StringMap a

O(min(n,L)) Insert with a combining function. If the key is already present in the map, the value of f new_value old_value will be inserted.

insertWithKey :: (Key -> a -> a -> a) -> Key -> a -> StringMap a -> StringMap a

O(min(n,L)) Insert with a combining function. If the key is already present in the map, the value of f key new_value old_value will be inserted.

Delete/Update

delete :: Key -> StringMap a -> StringMap a

O(min(n,L)) Delete an element from the map. If no element exists for the key, the map remains unchanged.

update :: (a -> Maybe a) -> Key -> StringMap a -> StringMap a

O(min(n,L)) Updates a value at a given key (if that key is in the trie) or deletes the element if the result of the updating function is Nothing. If the key is not found, the trie is returned unchanged.

updateWithKey :: (Key -> a -> Maybe a) -> Key -> StringMap a -> StringMap a

O(min(n,L)) Updates a value at a given key (if that key is in the trie) or deletes the element if the result of the updating function is Nothing. If the key is not found, the trie is returned unchanged.

Combine

Union

union :: StringMap a -> StringMap a -> StringMap a

O(n+m) Left-biased union of two maps. It prefers the first map when duplicate keys are encountered, i.e. (union == unionWith const).

unionWith :: (a -> a -> a) -> StringMap a -> StringMap a -> StringMap a

O(n+m) union with a combining function.

unionMapWith :: (b -> a) -> (a -> b -> a) -> StringMap a -> StringMap b -> StringMap a

Generalisation of unionWith. The second map may have another attribute type than the first one. Conversion and merging of the maps is done in a single step. This is much more efficient than mapping the second map and then call unionWith

unionWithConf to ( x y -> x op to y) m1 m2 = unionWith op m1 (fmap to m2)

unionWithKey :: (Key -> a -> a -> a) -> StringMap a -> StringMap a -> StringMap a

O(n+m) union with a combining function, including the key.

Difference

difference :: StringMap a -> StringMap b -> StringMap a

(O(min(n,m)) Difference between two string maps (based on keys).

differenceWith :: (a -> b -> Maybe a) -> StringMap a -> StringMap b -> StringMap a

(O(min(n,m)) difference with a combining function. If the combining function always returns Nothing, this is equal to proper set difference.

differenceWithKey :: (Key -> a -> b -> Maybe a) -> StringMap a -> StringMap b -> StringMap a

O(min(n,m)) difference with a combining function, including the key. If two equal keys are encountered, the combining function is applied to the key and both values. If it returns Nothing, the element is discarded, if it returns Just a value, the element is updated with the new value.

Interset

intersection :: StringMap a -> StringMap a -> StringMap a

O(min(n,m)) intersection is required to allow all major set operations: AND = intersection OR = union AND NOT = difference

intersectionWith :: (a -> b -> c) -> StringMap a -> StringMap b -> StringMap c

O(min(n,m)) intersection with a modification function

Traversal

Map

map :: (a -> b) -> StringMap a -> StringMap b

O(n) Map a function over all values in the string map.

mapWithKey :: (Key -> a -> b) -> StringMap a -> StringMap b

O(n) Same as map, but with an additional paramter

mapM :: Monad m => (a -> m b) -> StringMap a -> m (StringMap b)

Monadic map

mapWithKeyM :: Monad m => (Key -> a -> m b) -> StringMap a -> m (StringMap b)

Monadic mapWithKey

mapMaybe :: (a -> Maybe b) -> StringMap a -> StringMap b

O(n) Updates a value or deletes the element, if the result of the updating function is Nothing.

Folds

fold :: (a -> b -> b) -> b -> StringMap a -> b

Deprecated: use foldr instead

O(n) Fold over all values in the map.

foldWithKey :: (Key -> a -> b -> b) -> b -> StringMap a -> b

Deprecated: use foldrWithKey instead

O(n) Fold over all key/value pairs in the map.

Conversion

keys :: StringMap a -> [Key]

O(n) Returns all keys.

elems :: StringMap a -> [a]

O(n) Returns all values.

Lists

fromList :: [(Key, a)] -> StringMap a

O(n) Creates a string map from a list of key/value pairs.

toList :: StringMap a -> [(Key, a)]

O(n) Returns all elements as list of key value pairs,

toListShortestFirst :: StringMap v -> [(Key, v)]

returns all key-value pairs in breadth first order (short words first) this enables prefix search with upper bounds on the size of the result set e.g. search ... >>> toListShortestFirst >>> take 1000 will give the 1000 shortest words found in the result set and will ignore all long words

toList is derived from the following code found in the net when searching haskell breadth first search

Haskell Standard Libraray Implementation

 br :: Tree a -> [a]
 br t = map rootLabel $
        concat $
        takeWhile (not . null) $
        iterate (concatMap subForest) [t]

Maps

fromMap :: Map Key a -> StringMap a

O(n) Convert an ordinary map into a string map

toMap :: StringMap a -> Map Key a

O(n) Convert into an ordinary map.

Prefix and Fuzzy Search

prefixFilter :: Key -> StringMap a -> StringMap a

O(max(L,R)) Find all values where the string is a prefix of the key.

prefixFilterNoCase :: Key -> StringMap a -> StringMap a

Same as prefixFilterNoCase, bur case insensitive

lookupNoCase :: Key -> StringMap a -> StringMap a

Same as lookup, but case insensitive