Iterate set covered by cross-product of ranges in ruby
- by wilsona
I figured this answer had been asked before, so I searched, but I couldn't find anything. Granted, there are a ton of Ruby Array questions, so it might be there, just buried.
In any case, I'm trying to reduce a cross-product of ranges, returning a sum of all elements of the cross-product that meet some set of conditions. To construct a trivial example, if I have an array like this:
[0..1,0..1,0..1]
I'd like to iterate over this set:
[
[0,0,0],
[0,0,1],
[0,1,0],
[0,1,1],
[1,0,0],
[1,0,1],
[1,1,0],
[1,1,1]
]
and return a sum based the condition "return 1 if i[0] == 1 and i[2] == 0" (which would give 2). In my contrived example, I could do it like this:
br = 0..1
br.reduce(0){|sumx, x|
sumx + br.reduce(0){|sumy, y|
sumy + br.reduce(0){|sumz, z|
sumz + (x == 1 and z == 0 ? 1 : 0)
}
}
}
, but in the actual application, the set of ranges might be much larger, and nesting reduces that way would get quite ugly. Is there a better way?
