| Copyright | (c) The University of Glasgow 2001 |
|---|---|
| License | BSD-style (see the file libraries/base/LICENSE) |
| Maintainer | libraries@haskell.org |
| Stability | provisional |
| Portability | portable |
| Safe Haskell | Trustworthy |
| Language | Haskell2010 |
Data.Array
Description
Basic non-strict arrays.
Note: TheData.Array.IArray module provides a more general interface to immutable arrays: it defines operations with the same names as those defined below, but with more general types, and also definesArray instances of the relevant classes. To use that more general interface, importData.Array.IArray but notData.Array.
Haskell provides indexablearrays, which may be thought of as functionswhose domains are isomorphic to contiguous subsets of the integers.Functions restricted in this way can be implemented efficiently;in particular, a programmer may reasonably expect rapid access tothe components. To ensure the possibility of such an implementation,arrays are treated as data, not as general functions.
Since most array functions involve the classIx, this module is exportedfromData.Array so that modules need not import bothData.Array andData.Ix.
moduleData.Ix
The type of immutable non-strict (boxed) arrays with indices ini and elements ine.
| IArrayArray eSource# | |
Instance detailsDefined inData.Array.Base Methods bounds ::Ix i =>Array i e -> (i, i)Source# numElements ::Ix i =>Array i e ->Int unsafeArray ::Ix i => (i, i) -> [(Int, e)] ->Array i e unsafeAt ::Ix i =>Array i e ->Int -> e unsafeReplace ::Ix i =>Array i e -> [(Int, e)] ->Array i e unsafeAccum ::Ix i => (e -> e' -> e) ->Array i e -> [(Int, e')] ->Array i e unsafeAccumArray ::Ix i => (e -> e' -> e) -> e -> (i, i) -> [(Int, e')] ->Array i e | |
| Functor (Array i) | Since: base-2.1 |
| Foldable (Array i) | Since: base-4.8.0.0 |
Instance detailsDefined inData.Foldable Methods fold ::Monoid m =>Array i m -> m# foldMap ::Monoid m => (a -> m) ->Array i a -> m# foldMap' ::Monoid m => (a -> m) ->Array i a -> m# foldr :: (a -> b -> b) -> b ->Array i a -> b# foldr' :: (a -> b -> b) -> b ->Array i a -> b# foldl :: (b -> a -> b) -> b ->Array i a -> b# foldl' :: (b -> a -> b) -> b ->Array i a -> b# foldr1 :: (a -> a -> a) ->Array i a -> a# foldl1 :: (a -> a -> a) ->Array i a -> a# elem ::Eq a => a ->Array i a ->Bool# maximum ::Ord a =>Array i a -> a# | |
| Ix i =>Traversable (Array i) | Since: base-2.1 |
| (Ix i,Eq e) =>Eq (Array i e) | Since: base-2.1 |
| (Ix i,Ord e) =>Ord (Array i e) | Since: base-2.1 |
Instance detailsDefined inGHC.Arr | |
| (Ix a,Read a,Read b) =>Read (Array a b) | Since: base-2.1 |
| (Ix a,Show a,Show b) =>Show (Array a b) | Since: base-2.1 |
Arguments
| ::Ix i | |
| => (i, i) | a pair ofbounds, each of the index type of the array. These bounds are the lowest and highest indices in the array, in that order. For example, a one-origin vector of length |
| -> [(i, e)] | a list ofassociations of the form (index,value). Typically, this list will be expressed as a comprehension. An association |
| ->Array i e |
Construct an array with the specified bounds and containing values for given indices within these bounds.
The array is undefined (i.e. bottom) if any index in the list is out of bounds. The Haskell 2010 Report further specifies that if any two associations in the list have the same index, the value at that index is undefined (i.e. bottom). However in GHC's implementation, the value at such an index is the value part of the last association with that index in the list.
Because the indices must be checked for these errors,array is strict in the bounds argument and in the indices of the association list, but non-strict in the values. Thus, recurrences such as the following are possible:
a = array (1,100) ((1,1) : [(i, i * a!(i-1)) | i <- [2..100]])
Not every index within the bounds of the array need appear in the association list, but the values associated with indices that do not appear will be undefined (i.e. bottom).
If, in any dimension, the lower bound is greater than the upper bound, then the array is legal, but empty. Indexing an empty array always gives an array-bounds error, butbounds still yields the bounds with which the array was constructed.
listArray ::Ix i => (i, i) -> [e] ->Array i e#
Construct an array from a pair of bounds and a list of values in index order.
Arguments
| ::Ix i | |
| => (e -> a -> e) | accumulating function |
| -> e | initial value |
| -> (i, i) | bounds of the array |
| -> [(i, a)] | association list |
| ->Array i e |
TheaccumArray function deals with repeated indices in the association list using anaccumulating function which combines the values of associations with the same index.
For example, given a list of values of some index type,hist produces a histogram of the number of occurrences of each index within a specified range:
hist :: (Ix a, Num b) => (a,a) -> [a] -> Array a bhist bnds is = accumArray (+) 0 bnds [(i, 1) | i<-is, inRange bnds i]
accumArray is strict in each result of applying the accumulating function, although it is lazy in the initial value. Thus, unlike arrays built witharray, accumulated arrays should not in general be recursive.
(//) ::Ix i =>Array i e -> [(i, e)] ->Array i einfixl 9#
Constructs an array identical to the first argument except that it has been updated by the associations in the right argument. For example, ifm is a 1-origin,n byn matrix, then
m//[((i,i), 0) | i <- [1..n]]
is the same matrix, except with the diagonal zeroed.
Repeated indices in the association list are handled as forarray: Haskell 2010 specifies that the resulting array is undefined (i.e. bottom), but GHC's implementation uses the last association for each index.
accum ::Ix i => (e -> a -> e) ->Array i e -> [(i, a)] ->Array i e#
accum ff. ThusaccumArray can be defined usingaccum:
accumArray f z b = accum f (array b [(i, z) | i <- range b])
accum is strict in all the results of applying the accumulation. However, it is lazy in the initial values of the array.
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