Condition on a whole array


I have a fairly simple question that would like to sort out with your kind help :slight_smile: The fact is that I like quite a lot the conditional syntax
{something} ? true : false
which works great for short decissions like

x>0.5 ? 1 : 0

Is it possible to do something similar not for scalar valued x but for x a vector or array? How would that be done? I understand that


works, but what then? Of course I can use the map functionto do what I want, but was wondering if it is possible to do something simpler or performance wise (?)

Best regards and thanks,



How about

[v > 0.5 ? 1 : 0 for v in x]


The generator code above performs really well but ifelse seems to be even better:

julia> x = rand(100000);

julia> bar(x) = [v > 0.5 ? 1 : 0 for v in x]
bar (generic function with 1 method)

julia> @btime bar($x);
  103.453 μs (3 allocations: 781.34 KiB)

julia> foo(x) = ifelse.(x .> 0.5, 1, 0)
foo (generic function with 1 method)

julia> @btime foo($x);
  91.008 μs (2 allocations: 781.33 KiB)


Ahhh… that seems to be a vairly simple way, thanks :slight_smile: I’ll test both ways and check what is better for my needs…


One thing to keep in mind is that ifelse() and the ? operator are actually a bit different because ifelse evaluates both of its arguments, while ? only evaluates the argument chosen by the test. For example:

julia> function f(x)
         println("calling f")
f (generic function with 1 method)

julia> function g(x)
         println("calling g")
g (generic function with 1 method)

julia> y = true ? f(1) : g(1)
calling f

julia> y = ifelse(true, f(1), g(1))
calling f
calling g

It seems like this would make ifelse() always worse, but in fact the predictability of its behavior (always evaluating both arguments) can sometimes allow for more efficient pipelined code.


Oh thanks.

But anyway, I still wonder if there is a ‘dot’ notation for the ?
operator… Something of the form

x == 0 .? true : false


Regarding performance, you could try