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Add squeeze(A) method to squeeze all singleton dimensions #22000

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Add squeeze(A) method to squeeze all singleton dimensions #22000

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23 changes: 23 additions & 0 deletions base/abstractarraymath.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,29 @@ end

squeeze(A::AbstractArray, dim::Integer) = squeeze(A, (Int(dim),))

"""
squeeze(A)

Remove all singleton dimensions from array `A`.

```jldoctest
julia> a = reshape(collect(1:4),(2,2,1,1))
2×2×1×1 Array{Int64,4}:
[:, :, 1, 1] =
1 3
2 4

julia> squeeze(a)
2×2 Array{Int64,2}:
1 3
2 4
```
"""
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Perhaps add a warning re. the potential pitfalls of this method?

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I'm not sure what I would write? This function is incredibly straightforward; it removes all singleton dimensions.

Looking back over the previous discussion, it looks like the concern is that you may pass in an NxMxL matrix expecting L to equal 1, but then being surprised when M also happened to equal 1 and thus the result is a 1-dimensional array. I'm not sure how to make the docstring more explicit that such a thing will happen; that is, after all, the entire point of this function.

function squeeze(A::AbstractArray)
singleton_dims = tuple((d for d in 1:ndims(A) if size(A, d) == 1)...)
return squeeze(A, singleton_dims)
end


## Unary operators ##

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8 changes: 8 additions & 0 deletions test/subarray.jl
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Expand Up @@ -555,3 +555,11 @@ let
@test Base.IndexStyle(view(a, :, :)) == Base.IndexLinear()
@test isbits(view(a, :, :))
end

# issue
# Ensure that we can auto-squeeze out all singleton dimensions of an array
let
@test ndims(squeeze(ones(10, 1, 1))) == 1
@test ndims(squeeze(ones(1, 10))) == 1
@test ndims(squeeze(ones(10, 10))) == 2
end