I was wondering how you can sum from one point of an array to another point, for example:
array = [1,3,5,6,1]
assuming i is a moving variable, for example
i = 2
assuming k is a moving variable, for example
k = 4
The solution I'm looking for is to sum from array[2] to array[4], so 5+6+1 = 12
I've tried using (array[i]..array[k]).reduce(:+) but it doesn't seem to work.
Any help is appreciated!
Almost! But you're creating a range between two integer array values when you want to be indexing an array!
array[i..k].reduce(:+)
The solution given by @glennmcdonald is the normal way to do a partial sum, but it does create another array:
array[first_index..last_index]
If that array is sufficiently large, you may prefer or be required to compute the sum without creating a new array. Here are two of many ways you could do that:
def sum_range1(array, first_index, last_index)
(first_index..last_index).reduce(0) { |tot,i| tot+array[i] }
end
or this:
def sum_range2(array, first_index, last_index)
array.each_with_index.reduce(0) { |tot,(n,i)|
tot + ((first_index..last_index).cover?(i) ? n : 0) }
end
arr = [1,3,5,6,1]
sum_range1(arr, 2, 4) #=> 12
sum_range2(arr, 2, 4) #=> 12
