CODEWITHSUNDEEP
juliaarray-indexing
Fredrik P
Fredrik P

Reputation: 694

Subdimensional array from multidimensional array in Julia

With NumPy I can access a subdimensional array from a multidimensional array without knowing the dimension of the original array:

import numpy as np
a = np.zeros((2, 3, 4))  # A 2-by-3-by-4 array of zeros
a[0]  # A 3-by-4 array of zeros

but with Julia I am at a loss. It seems that I must know the dimension of a to do this:

a = zeros(2, 3, 4)  # A 2-by-3-by-4 array of zeros
a[1, :, :]  # A 3-by-4 array of zeros

What should I do if I don't know the dimension of a?

Upvotes: 2

Views: 140

Answers (2)

Sundar R
Sundar R

Reputation: 14735

If you want to iterate over each "subdimensional array" in order, you can also use eachslice:

julia> a = reshape(1:24, (2, 3, 4));

julia> eachslice(a, dims = 1) |> first
3×4 view(reshape(::UnitRange{Int64}, 2, 3, 4), 1, :, :) with eltype Int64:
 1   7  13  19
 3   9  15  21
 5  11  17  23

julia> for a2dims in eachslice(a, dims = 1)
         @show size(a2dims)
       end
size(a2dims) = (3, 4)
size(a2dims) = (3, 4)

Upvotes: 1

هنروقتان
هنروقتان

Reputation: 788

selectdim gives a view of what you are looking for,

a = zeros(2, 3, 4)
selectdim(a,1,1)

Upvotes: 3

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