How can i convert number string array to int array

General Usage
1

Need help to convert string number array to int array

Like
[“0”, “1”, “0”, “1”, “0”, “1”, “1”, “1”] To [0, 1, 0, 1, 0, 1, 1, 1]

NB: Without use this code
[parse(Int, x) for x in array]
because this method is too slow in big array [array size about 1 million +]

2

You could potentially convert it to a categorical array first.

1 Like
3

Is it really a problem?

julia> A = [string(rand(1:1000)) for _ in 1:1_000_000];

julia> @btime parse.(Int, $A);
  27.091 ms (2 allocations: 7.63 MiB)
3 Likes
4

It seems like these two methods are equally fast:

julia> a = rand(("0", "1"), 10^6);

julia> @btime [parse(Int, x) for x in $a];
  36.087 ms (3 allocations: 7.63 MiB)

julia> @btime parse.(Int, $a);
  35.576 ms (2 allocations: 7.63 MiB)

It seems pretty fast to me.

If, however, the inputs are Chars instead of Strings, it can get faster:

julia> c = rand('0':'1', 10^6);

julia> @btime parse.(Int, $c);
  8.302 ms (2 allocations: 7.63 MiB)

or even

julia> @btime Int.($c) .- 48;
  2.241 ms (2 allocations: 7.63 MiB)

Here’s another one, if Int8 is ok:

julia> @btime Int8.($c) .- Int8(48);
  784.793 μs (2 allocations: 976.70 KiB)
2 Likes
5

If you don’t need to validate inputs and these are the only two options, something like

parse01(str) = str == "1" ? 1 : 0

could work, eg

julia> @btime parse01.($a);
  4.704 ms (2 allocations: 7.63 MiB)

but, like the others contributing to this topic, I wonder if this is really the bottleneck in your code. I would go with parse(Int, ...) as the cost is trivial in any case, and it is robust and readable.