[Haskell-cafe] A numpy equivalent for Haskell

[Ivan Lazar Miljenovic]

Did you know about hmatrix (available on Hackage) before you wrote this?

"yairchu at gmail.com" <yairchu at gmail.com> writes:

> Hi Cafe,
>
> I've created a numpy equivalent for Haskell. (Numpy is a python
> library for multi-dimensional arrays and operations on them)
>
> Code at http://github.com/yairchu/numkell
> (not yet on hackage because it needs better names)
>
> A numkell array is a pair of a function from integer inputs and a
> range for its inputs (size).
> This allows for easy memoizing into in-memory arrays, and
> additionally, numkell arrays also support useful operations like
> numpy's newaxis and folding axes away.
> As the "Array" name was already taken, numkell's array is currently
> called "Funk" (name suggestions very appreciated).
>
> An example:
> Given an bunch of vectors as a 2d array, compute the distance between
> each pair of vectors
>
> {-# LANGUAGE DeriveDataTypeable, GeneralizedNewtypeDeriving,
> TypeOperators #-}
>
> import Data.HList
> import Data.NumKell
> import Data.Typeable
>
> newtype PersonIdx = PersonIdx Int
>   deriving (Enum, Eq, Integral, Num, Ord, Real, Show, Typeable)
>
> newtype FeatureIdx = FeatureIdx Int
>   deriving (Enum, Eq, Integral, Num, Ord, Real, Show, Typeable)
>
> let personProps = fFromList [[5,3,2],[4,8,1],[2,6,9],[5,3,0]] :: Funk
> (HJust PersonIdx :*: HJust FeatureIdx :*: HNil) Double
>
>> personProps
>           FeatureIdx   0   1   2
> PersonIdx          +   -   -   -
>         0          | 5.0 3.0 2.0
>         1          | 4.0 8.0 1.0
>         2          | 2.0 6.0 9.0
>         3          | 5.0 3.0 0.0
>
>> sumAxes (fmap (** 2) (liftF2 (-) (personProps !/ (SNewAxis .*. HNil)) (personProps !/ (SAll .*. SNewAxis .*. HNil)))) (TFalse .*. TFalse .*. TTrue .*. HNil)
>
>           PersonIdx    0    1    2    3
> PersonIdx         +    -    -    -    -
>         0         |  0.0 27.0 67.0  4.0
>         1         | 27.0  0.0 72.0 27.0
>         2         | 67.0 72.0  0.0 99.0
>         3         |  4.0 27.0 99.0  0.0
>
> In Python the last line looks shorter:
>
>>>> ((personProps[newaxis] - personProps[:,newAxis]) ** 2).sum(2)
>
> Mostly due to Python's slicing syntax sugar.
> Still, numkell has one large benefit over numpy (apart from being for
> Haskell): With numpy this example creates a temporary 3d array in
> memory. In numkell the array is not allocated in memory unless "fMemo"
> is called.
>
> If anyone has comments, suggestions, naming suggestions, complaints,
> etc, I would very much like to hear.
>
> cheers,
> Yair
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-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
IvanMiljenovic.wordpress.com