Is there usage of Haskell Repa slice function analogous to Vector and other languages?

I am trying to get a usable version of multidimensional arrays in Haskell, comparable to that of numpy arrays in Python and other languages.
I found other questions about how to write custom functions for arrays of specific dimensions, but my objective it more to the point, get a similar behavior of Data.Vector's slice function, which is intuitive and does the job of bracket-indexed arrays of other languages.

Vector's slice function has type
V.slice :: Int -> Int -> V.Vector a -> V.Vector a

so slicing a vector v is as simple as

import Data.Vector as V

let v = V.fromList [1..10]

    i = 1

    j = 5

V.slice i j v

Repa's slice on the other hand has type

R.slice :: (R.Slice sl, R.Shape (R.FullShape sl), R.Source r e) => R.Array r (R.FullShape sl) e -> sl -> R.Array R.D (R.SliceShape sl) e

so it takes a Repa array and a shape and return a delayed array.
I understand that Repa does not take Integers as indices, but I am looking for a general use of the slice function for arbitrary dimension, whether using Repa's (Z :. i) or ixn dimension specification.

I'm not looking for a dimension-dependent function using traverse, and would prefer not to go into any template haskell to generalize that, although if it's not possible to use the slice function generally it is what it is.

The question is, then: is it possible to use Repa's slice function to get arbitrary slices of multidimensional arrays, like in numpy's v[x1:x2,y1:y2] or C++ Eigen's matrix.block<p,q>(i,j)?

edited Nov 26 '18 at 4:18

Alexis King

32.3k1196166

asked Nov 26 '18 at 1:40

Twisted Mersenne

274

numpy's v[x1:x2,y1:y2] means to get the elements of index (1,1), (1,2), (2,1), (2,2) and return the result as 2 x 2 metrix?

– assembly.jc
Nov 26 '18 at 10:46

It means getting all elements in the first dimension (which I'm calling x) between indices x1 and x2, and the second dimension (y) between y1 and y2. In Python getting those elements you mention would be then x1,x2 = y1,y2 = 1,3, or v[1:3,1:3], which would be a 2x2 matrix indeed since numpy arrays don't include the last index. In Haskell V.slice 1 2 v would do the analogous operation for a single dimension, but doing that for 2 or more is not straightforwardly described in Repa's tutorial or documentation

– Twisted Mersenne
Nov 26 '18 at 16:48

add a comment |

Vector's slice function has type
V.slice :: Int -> Int -> V.Vector a -> V.Vector a

so slicing a vector v is as simple as

import Data.Vector as V

let v = V.fromList [1..10]

    i = 1

    j = 5

V.slice i j v

Repa's slice on the other hand has type

R.slice :: (R.Slice sl, R.Shape (R.FullShape sl), R.Source r e) => R.Array r (R.FullShape sl) e -> sl -> R.Array R.D (R.SliceShape sl) e

The question is, then: is it possible to use Repa's slice function to get arbitrary slices of multidimensional arrays, like in numpy's v[x1:x2,y1:y2] or C++ Eigen's matrix.block<p,q>(i,j)?

edited Nov 26 '18 at 4:18

Alexis King

32.3k1196166

asked Nov 26 '18 at 1:40

Twisted Mersenne

274

numpy's v[x1:x2,y1:y2] means to get the elements of index (1,1), (1,2), (2,1), (2,2) and return the result as 2 x 2 metrix?

– assembly.jc
Nov 26 '18 at 10:46

It means getting all elements in the first dimension (which I'm calling x) between indices x1 and x2, and the second dimension (y) between y1 and y2. In Python getting those elements you mention would be then x1,x2 = y1,y2 = 1,3, or v[1:3,1:3], which would be a 2x2 matrix indeed since numpy arrays don't include the last index. In Haskell V.slice 1 2 v would do the analogous operation for a single dimension, but doing that for 2 or more is not straightforwardly described in Repa's tutorial or documentation

– Twisted Mersenne
Nov 26 '18 at 16:48

add a comment |

Vector's slice function has type
V.slice :: Int -> Int -> V.Vector a -> V.Vector a

so slicing a vector v is as simple as

import Data.Vector as V

let v = V.fromList [1..10]

    i = 1

    j = 5

V.slice i j v

Repa's slice on the other hand has type

R.slice :: (R.Slice sl, R.Shape (R.FullShape sl), R.Source r e) => R.Array r (R.FullShape sl) e -> sl -> R.Array R.D (R.SliceShape sl) e

The question is, then: is it possible to use Repa's slice function to get arbitrary slices of multidimensional arrays, like in numpy's v[x1:x2,y1:y2] or C++ Eigen's matrix.block<p,q>(i,j)?

edited Nov 26 '18 at 4:18

Alexis King

32.3k1196166

asked Nov 26 '18 at 1:40

Twisted Mersenne

274

Vector's slice function has type
V.slice :: Int -> Int -> V.Vector a -> V.Vector a

so slicing a vector v is as simple as

import Data.Vector as V

let v = V.fromList [1..10]

    i = 1

    j = 5

V.slice i j v

Repa's slice on the other hand has type

R.slice :: (R.Slice sl, R.Shape (R.FullShape sl), R.Source r e) => R.Array r (R.FullShape sl) e -> sl -> R.Array R.D (R.SliceShape sl) e

The question is, then: is it possible to use Repa's slice function to get arbitrary slices of multidimensional arrays, like in numpy's v[x1:x2,y1:y2] or C++ Eigen's matrix.block<p,q>(i,j)?

arrays haskell vector repa

edited Nov 26 '18 at 4:18

Alexis King

32.3k1196166

asked Nov 26 '18 at 1:40

Twisted Mersenne

274

edited Nov 26 '18 at 4:18

Alexis King

32.3k1196166

asked Nov 26 '18 at 1:40

Twisted Mersenne

274

edited Nov 26 '18 at 4:18

Alexis King

32.3k1196166

edited Nov 26 '18 at 4:18

Alexis King

32.3k1196166

edited Nov 26 '18 at 4:18

Alexis King

32.3k1196166

asked Nov 26 '18 at 1:40

Twisted Mersenne

274

asked Nov 26 '18 at 1:40

Twisted Mersenne

274

asked Nov 26 '18 at 1:40

Twisted Mersenne

274

numpy's v[x1:x2,y1:y2] means to get the elements of index (1,1), (1,2), (2,1), (2,2) and return the result as 2 x 2 metrix?

– assembly.jc
Nov 26 '18 at 10:46

It means getting all elements in the first dimension (which I'm calling x) between indices x1 and x2, and the second dimension (y) between y1 and y2. In Python getting those elements you mention would be then x1,x2 = y1,y2 = 1,3, or v[1:3,1:3], which would be a 2x2 matrix indeed since numpy arrays don't include the last index. In Haskell V.slice 1 2 v would do the analogous operation for a single dimension, but doing that for 2 or more is not straightforwardly described in Repa's tutorial or documentation

– Twisted Mersenne
Nov 26 '18 at 16:48

add a comment |

numpy's v[x1:x2,y1:y2] means to get the elements of index (1,1), (1,2), (2,1), (2,2) and return the result as 2 x 2 metrix?

– assembly.jc
Nov 26 '18 at 10:46

It means getting all elements in the first dimension (which I'm calling x) between indices x1 and x2, and the second dimension (y) between y1 and y2. In Python getting those elements you mention would be then x1,x2 = y1,y2 = 1,3, or v[1:3,1:3], which would be a 2x2 matrix indeed since numpy arrays don't include the last index. In Haskell V.slice 1 2 v would do the analogous operation for a single dimension, but doing that for 2 or more is not straightforwardly described in Repa's tutorial or documentation

– Twisted Mersenne
Nov 26 '18 at 16:48

numpy's v[x1:x2,y1:y2] means to get the elements of index (1,1), (1,2), (2,1), (2,2) and return the result as 2 x 2 metrix?

– assembly.jc
Nov 26 '18 at 10:46

It means getting all elements in the first dimension (which I'm calling x) between indices x1 and x2, and the second dimension (y) between y1 and y2. In Python getting those elements you mention would be then x1,x2 = y1,y2 = 1,3, or v[1:3,1:3], which would be a 2x2 matrix indeed since numpy arrays don't include the last index. In Haskell V.slice 1 2 v would do the analogous operation for a single dimension, but doing that for 2 or more is not straightforwardly described in Repa's tutorial or documentation

– Twisted Mersenne
Nov 26 '18 at 16:48

add a comment |

1 Answer
1

active

oldest

votes

I believe the closest equivalent is extract, which takes a starting index (like ix2 x1 y1) and a size (like ix2 (x2-x1) (y2-y1)).

The result of extract always has the same number of dimensions as the input, but can have different size in each dimension. The result of slice can have a different number of dimensions, but in any given dimension it takes either all elements or exactly one. (Based on the instances for Shape and Slice.)

answered Nov 26 '18 at 18:14

bergey

2,443717

Thanks. That seems to work alright.. Still pretty cumbersome compared to other languages and even to Vector.slice. I can deal with the array keeping the same number of dimensions and size 1 along the dimension of the slice, it's not ideal but workable in the absence of analog usage of Repa.slice.

– Twisted Mersenne
Dec 1 '18 at 4:24

add a comment |

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1 Answer
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active

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1 Answer
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active

oldest

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I believe the closest equivalent is extract, which takes a starting index (like ix2 x1 y1) and a size (like ix2 (x2-x1) (y2-y1)).

answered Nov 26 '18 at 18:14

bergey

2,443717

Thanks. That seems to work alright.. Still pretty cumbersome compared to other languages and even to Vector.slice. I can deal with the array keeping the same number of dimensions and size 1 along the dimension of the slice, it's not ideal but workable in the absence of analog usage of Repa.slice.

– Twisted Mersenne
Dec 1 '18 at 4:24

add a comment |

I believe the closest equivalent is extract, which takes a starting index (like ix2 x1 y1) and a size (like ix2 (x2-x1) (y2-y1)).

answered Nov 26 '18 at 18:14

bergey

2,443717

Thanks. That seems to work alright.. Still pretty cumbersome compared to other languages and even to Vector.slice. I can deal with the array keeping the same number of dimensions and size 1 along the dimension of the slice, it's not ideal but workable in the absence of analog usage of Repa.slice.

– Twisted Mersenne
Dec 1 '18 at 4:24

add a comment |

I believe the closest equivalent is extract, which takes a starting index (like ix2 x1 y1) and a size (like ix2 (x2-x1) (y2-y1)).

answered Nov 26 '18 at 18:14

bergey

2,443717

I believe the closest equivalent is extract, which takes a starting index (like ix2 x1 y1) and a size (like ix2 (x2-x1) (y2-y1)).

answered Nov 26 '18 at 18:14

bergey

2,443717

answered Nov 26 '18 at 18:14

bergey

2,443717

answered Nov 26 '18 at 18:14

bergey

2,443717

answered Nov 26 '18 at 18:14

bergey

2,443717

Thanks. That seems to work alright.. Still pretty cumbersome compared to other languages and even to Vector.slice. I can deal with the array keeping the same number of dimensions and size 1 along the dimension of the slice, it's not ideal but workable in the absence of analog usage of Repa.slice.

– Twisted Mersenne
Dec 1 '18 at 4:24

add a comment |

Thanks. That seems to work alright.. Still pretty cumbersome compared to other languages and even to Vector.slice. I can deal with the array keeping the same number of dimensions and size 1 along the dimension of the slice, it's not ideal but workable in the absence of analog usage of Repa.slice.

– Twisted Mersenne
Dec 1 '18 at 4:24

Thanks. That seems to work alright.. Still pretty cumbersome compared to other languages and even to Vector.slice. I can deal with the array keeping the same number of dimensions and size 1 along the dimension of the slice, it's not ideal but workable in the absence of analog usage of Repa.slice.

– Twisted Mersenne
Dec 1 '18 at 4:24

add a comment |

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