Round inplace?

General Usage
1

What is the reason that there are not round! functions? Is it not possible to do that type of operation in place? It seems like it is no different than replace! (which exists) and the thing you are replacing with is simply a rounded version of the original value (without the need to search for it).

2

No operations on floating-point numbers are in-place since they are immutable.

1 Like
3

Sorry, I mean for vectors

4

Because its not common to need it and it’s a one-liner to write it yourself using broadcasting, I guess.

v .= round.(v)

4 Likes
5

Fair enough. I am rounding a vector with >100M values so it takes a bit to finish and so this came to mind.

6

replace! isn’t so easy to replace with a dotted version, while in-place round is trivial to write with dots.

7

I guess the real question is why you need this – i.e. what you will do with the 100M results.

8

It is worth noting that the @dpsanders answer use dot fusion to not create an intermediary array so, in that aspect, it is as efficient as a round! could get.

1 Like
9

Almost:

julia> function round1!(v)
           v .= round.(v)
       end
round1! (generic function with 1 method)

julia> function round2!(v)
       for i in eachindex(v)
           v[i] = round(v[i])
       end
       end
round2! (generic function with 1 method)

julia> v = 10 .* rand(1000);

julia> function round2!(v)
       for i in eachindex(v)
           @inbounds v[i] = round(v[i])
       end
       end
round2! (generic function with 1 method)

julia> @btime round1!($v);
  69.519 ns (0 allocations: 0 bytes)

julia> @btime round2!($v);
  66.269 ns (0 allocations: 0 bytes)
10

Ok, but:

julia> using BenchmarkTools
julia> function round1!(v)
           @inbounds v .= round.(v)
       end
julia> function round2!(v)
           for i in eachindex(v)
               @inbounds v[i] = round(v[i])
           end
       end
julia> import Random
julia> Random.seed!(0);
julia> v = 1000 .* rand(100000);
julia> @btime round1!($v)
  20.245 μs (0 allocations: 0 bytes)
julia> @btime round2!($v)
  19.232 μs (0 allocations: 0 bytes)
julia> @btime round1!($v)
  19.132 μs (0 allocations: 0 bytes)
julia> @btime round2!($v)
  19.166 μs (0 allocations: 0 bytes)
julia> @btime round1!($v)
  19.512 μs (0 allocations: 0 bytes)
julia> @btime round2!($v)
  19.248 μs (0 allocations: 0 bytes

Seems negligible to me.

2 Likes