I have a pair of arrays,
array_1 = [1,2,3,4,5]
array_2 = [10,9,8,7,6]
and I'm trying to subtract the nth element of one array from the (n-1)-th element of the second array, starting with the n-th element, yielding an array of:
[9-1, 8-2, 7-3, 6-4] = [8, 6, 4, 2]
I wrote it in a procedural fashion:
array_1.pop
array_2.shift
[array_2,array_1].transpose.map { |a,b| a-b }
but I do not wish to alter the arrays. Is there a method or another way to go about this?
Another way:
enum1 = array_1.to_enum
enum2 = array_2.to_enum
enum2.next
arr = []
loop do
arr << enum2.next - enum1.next
end
arr
#=> [8, 6, 4, 2]
StopIteration exception when an attempt is made to advance the enumerator beyond its end. (Same for peek.) The exception is handled by Kernel#loop by breaking out of the loop.Use the non-destructive drop for the receiver, and zip, which will stop when the receiver runs out of an element even if the argument has more.
array_2.drop(1).zip(array_1).map{|a, b| a - b}
I think you may be overthinking it a bit; as long as both arrays are the same length, you can just iterate over the indices you care about, and reference the other array by index - offset.
array_1 = [1,2,3,4,5]
array_2 = [10,9,8,7,6]
n = 1
(n...array_1.length).map {|i| array_2[i] - array_1[i - 1] }
You can set n to whatever number you like and compute from that point onwards, so even if the arrays were tremendously large, you don't have to generate any intermediate arrays, and you don't have to perform any unnecessary work.
[array_2[1..-1], array_1[0..-2]].transpose.map { |a,b| a-b } #=> [8, 6, 4, 2].