Haskell Language Vectors


It [Data.Vector] has an emphasis on very high performance through loop fusion, whilst retaining a rich interface. The main data types are boxed and unboxed arrays, and arrays may be immutable (pure), or mutable. Arrays may hold Storable elements, suitable for passing to and from C, and you can convert between the array types. Arrays are indexed by non-negative Int values.

The Haskell Wiki has these recommendations:

In general:

  • End users should use Data.Vector.Unboxed for most cases
  • If you need to store more complex structures, use Data.Vector
  • If you need to pass to C, use Data.Vector.Storable

For library writers;

  • Use the generic interface, to ensure your library is maximally flexible: Data.Vector.Generic

The Data.Vector Module

The Data.Vector module provided by the vector is a high performance library for working with arrays.

Once you've imported Data.Vector, it's easy to start using a Vector:

Prelude> import Data.Vector
Prelude Data.Vector> let a = fromList [2,3,4]
Prelude Data.Vector> a
fromList [2,3,4] :: Data.Vector.Vector
Prelude Data.Vector> :t a
a :: Vector Integer

You can even have a multi-dimensional array:

Prelude Data.Vector> let x = fromList [ fromList [1 .. x] | x <- [1..10] ]
Prelude Data.Vector> :t x
x :: Vector (Vector Integer)

Filtering a Vector

Filter odd elements:

Prelude Data.Vector> Data.Vector.filter odd y
fromList [1,3,5,7,9,11] :: Data.Vector.Vector

Mapping (`map`) and Reducing (`fold`) a Vector

Vectors can be map'd and fold'd,filter'd andzip`'d:

Prelude Data.Vector> Data.Vector.map (^2) y
fromList [0,1,4,9,16,25,36,49,64,81,100,121] :: Data.Vector.Vector

Reduce to a single value:

Prelude Data.Vector> Data.Vector.foldl (+) 0 y

Working on Multiple Vectors

Zip two arrays into an array of pairs:

Prelude Data.Vector> Data.Vector.zip y y
fromList [(0,0),(1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8),(9,9),(10,10),(11,11)] :: Data.Vector.Vector