Is there a function to clip an array to a maximum value? e.g. set values in an arr

General Usage
1

Is there a function to clip an array to a maximum value? e.g. set values in an array greater than 1.0 to 1.0

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2

Yup, it’s called clamp!:

help?> clamp!
search: clamp! clamp

  clamp!(array::AbstractArray, lo, hi)

  Restrict values in array to the specified range, in-place. See also clamp.
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3

Just for clamping the maximum, and not the minimum, you can use

x .= min.(x, hi)
4

I wonder why we kept the clamp! function, given that it seems equivalent to

array .= clamp.(array, lo, hi)

Probably it was just an oversight that it didn’t get removed when we removed the other vectorized functions in favor of dot calls?

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5

Yeah, I was actually surprised to find it as well–it does feel like a vestige from the era before broadcasting.

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6

The redundancy has been mentioned before in stackoverflow.

Curiously, I get different timing for clamp vs. clamp!:

using BenchmarkTools
X0 = randn(100,100); X = copy(X0);
@btime clamp!($X, -0.5, 0.5);
#  1.803 μs (0 allocations: 0 bytes)
clampme!(X, lo, hi) = X .= clamp.(X, lo, hi)
X = copy(X0);
@btime clampme!($X, -0.5, 0.5);
#  9.515 μs (0 allocations: 0 bytes)

It seems that clamp! does an @inbounds loop, and perhaps broadcasting fails to do it automatically. Or perhaps this is user benchmarking error.

7

I think slowness may be related to this issue

8

I don’t think so, since that issue is for 1d arrays, but in this case it’s almost the same speed for 1d arrays:

julia> X = randn(100*100);

julia> @btime clamp!($X, -0.5, 0.5);
  1.723 μs (0 allocations: 0 bytes)

julia> @btime clampme!($X, -0.5, 0.5);
  1.721 μs (0 allocations: 0 bytes)

It seems to be specific to broadcast loops for 2d (or more) arrays.

9

3 posts were split to a new topic: Understanding in-place broadcasting syntax (.=)

11

I think this is 43153, broadcasts which re-use an array.

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