List comprehension for running total

Question

I want to get a running total from a list of numbers.

For demo purposes, I start with a sequential list of numbers using range

a = range         


        

Answer 1

Here's a linear time solution one liner:

list(reduce(lambda (c,s), a: (chain(c,[s+a]), s+a), l,(iter([]),0))[0])

Example:

l = range(10)
list(reduce(lambda (c,s), a: (chain(c,[s+a]), s+a), l,(iter([]),0))[0])
>>> [0, 1, 3, 6, 10, 15, 21, 28, 36, 45]

In short, the reduce goes over the list accumulating sum and constructing an list. The final x[0] returns the list, x[1] would be the running total value.