4 ms·

What's the deal with the lack of conditionals in comprehensions? Is there a good reason that the Julia devs didn't include that, or is it just something that's

• omaranto 12y ago
  Julia's comprehensions are multidimensional array comprehensions so allowing filtering doesn't make much sense because the result needs to be rectangular and filtering can create arbitrary holes. For a one-dimensional array comprehension it does make sense to allow filtering and this can be easily expressed in Julia by making a coroutine that produces the values and collecting its output in an array. Multidimensional (here multi=2) array result: julia> [i+j for i=1:3, j=1:3] 3x3 Array{Int32,2}: 2 3 4 3 4 5 4 5 6 One dimensional array result, with filtering: julia> collect(@task for i=1:6; if i%3>0; produce(i); end; end) 4-element Array{Any,1}: 1 2 4 5 Notice that this last technique is more powerful than typical comprehensions, since it doesn't just add the possibility of filtering but arbitrary code to generate the elements.
  • irremediable 12y ago
    Thanks for the further info! I'd managed to figure out that it was because of multidimensional arrays (that snippet I quoted) but I didn't immediately see a nice way to achieve the same thing. And now, because you posted it, I do. I'll have to give Julia a go. :)