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

Foldable 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) TODO: INTERNAL

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)]

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)]

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

Construction

empty :: StringMap v

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.

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 tries (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.

Traversal

Map

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

O(n) Map a function over all values in the prefix tree.

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

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

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

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

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

Conversion

keys :: StringMap a -> [Key]

O(n) Returns all values.

elems :: StringMap a -> [a]

O(n) Returns all values.

Lists

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

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

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

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

toListBF :: 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 ... >>> toListBF >>> 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 Prefix tree

toMap :: StringMap a -> Map Key a

O(n) Convert into an ordinary map.

Debugging

space :: StringMap a -> Int

space required by a prefix tree (logically)

Singletons are counted as 0, all other n-ary constructors are counted as n+1 (1 for the constructor and 1 for every field) cons nodes of char lists are counted 2, 1 for the cons, 1 for the char for values only the ref to the value is counted, not the space for the value itself key chars are assumed to be unboxed

keyChars :: StringMap a -> Int

Prefix and Fuzzy Search

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

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

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

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

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

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

O(max(L,R)) Find all values where the string is a prefix of the key. Breadth first variant, short words first in the result list

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

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