array-0.3.0.2: Mutable and immutable arrays

Portabilitynon-portable (uses Data.Array.Base)
Stabilityexperimental
Maintainer[email protected]

Data.Array.IArray

Contents

Description

Immutable arrays, with an overloaded interface. For array types which can be used with this interface, see the Array type exported by this module and the Data.Array.Unboxed module. Other packages, such as diffarray, also provide arrays using this interface.

Synopsis

Array classes

class IArray a e whereSource

Class of immutable array types.

An array type has the form (a i e) where a is the array type constructor (kind * -> * -> *), i is the index type (a member of the class Ix), and e is the element type. The IArray class is parameterised over both a and e, so that instances specialised to certain element types can be defined.

Methods

bounds :: Ix i => a i e -> (i, i)Source

Extracts the bounds of an immutable array

module Data.Ix

Immutable non-strict (boxed) arrays

data Ix i => Array i e Source

The type of immutable non-strict (boxed) arrays with indices in i and elements in e.

Instances

Typeable2 Array 
IArray Array e 
Ix i => Functor (Array i) 
(Ix i, Eq e) => Eq (Array i e) 
(Ix i, Ord e) => Ord (Array i e) 
(Ix a, Show a, Show b) => Show (Array a b) 

Array construction

arraySource

Arguments

:: (IArray a e, Ix i) 
=> (i, i)

bounds of the array: (lowest,highest)

-> [(i, e)]

list of associations

-> a i e 

Constructs an immutable array from a pair of bounds and a list of initial associations.

The bounds are specified as a pair of the lowest and highest bounds in the array respectively. For example, a one-origin vector of length 10 has bounds (1,10), and a one-origin 10 by 10 matrix has bounds ((1,1),(10,10)).

An association is a pair of the form (i,x), which defines the value of the array at index i to be x. The array is undefined if any index in the list is out of bounds. If any two associations in the list have the same index, the value at that index is implementation-dependent. (In GHC, the last value specified for that index is used. Other implementations will also do this for unboxed arrays, but Haskell 98 requires that for Array the value at such indices is bottom.)

Because the indices must be checked for these errors, array is strict in the bounds argument and in the indices of the association list. Whether array is strict or non-strict in the elements depends on the array type: Data.Array.Array is a non-strict array type, but all of the Data.Array.Unboxed.UArray arrays are strict. Thus in a non-strict array, 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.

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, but bounds still yields the bounds with which the array was constructed.

listArray :: (IArray a e, Ix i) => (i, i) -> [e] -> a i eSource

Constructs an immutable array from a list of initial elements. The list gives the elements of the array in ascending order beginning with the lowest index.

accumArraySource

Arguments

:: (IArray a e, Ix i) 
=> (e -> e' -> e)

An accumulating function

-> e

A default element

-> (i, i)

The bounds of the array

-> [(i, e')]

List of associations

-> a i e

Returns: the array

Constructs an immutable array from a list of associations. Unlike array, the same index is allowed to occur multiple times in the list of associations; an accumulating function is used to combine the values of elements 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 b
 hist bnds is = accumArray (+) 0 bnds [(i, 1) | i\<-is, inRange bnds i]

Accessing arrays

(!) :: (IArray a e, Ix i) => a i e -> i -> eSource

Returns the element of an immutable array at the specified index.

indices :: (IArray a e, Ix i) => a i e -> [i]Source

Returns a list of all the valid indices in an array.

elems :: (IArray a e, Ix i) => a i e -> [e]Source

Returns a list of all the elements of an array, in the same order as their indices.

assocs :: (IArray a e, Ix i) => a i e -> [(i, e)]Source

Returns the contents of an array as a list of associations.

Incremental array updates

(//) :: (IArray a e, Ix i) => a i e -> [(i, e)] -> a i eSource

Takes an array and a list of pairs and returns an array identical to the left argument except that it has been updated by the associations in the right argument. For example, if m is a 1-origin, n by n matrix, then m//[((i,i), 0) | i <- [1..n]] is the same matrix, except with the diagonal zeroed.

As with the array function, if any two associations in the list have the same index, the value at that index is implementation-dependent. (In GHC, the last value specified for that index is used. Other implementations will also do this for unboxed arrays, but Haskell 98 requires that for Array the value at such indices is bottom.)

For most array types, this operation is O(n) where n is the size of the array. However, the diffarray package provides an array type for which this operation has complexity linear in the number of updates.

accum :: (IArray a e, Ix i) => (e -> e' -> e) -> a i e -> [(i, e')] -> a i eSource

accum f takes an array and an association list and accumulates pairs from the list into the array with the accumulating function f. Thus accumArray can be defined using accum:

 accumArray f z b = accum f (array b [(i, z) | i \<- range b])

Derived arrays

amap :: (IArray a e', IArray a e, Ix i) => (e' -> e) -> a i e' -> a i eSource

Returns a new array derived from the original array by applying a function to each of the elements.

ixmap :: (IArray a e, Ix i, Ix j) => (i, i) -> (i -> j) -> a j e -> a i eSource

Returns a new array derived from the original array by applying a function to each of the indices.