Reference · Vectors

vec.cumsum

vec.cumsum(list | null) -> list

What it does

The running total: a list where each item is the sum of the input up to and including that position. The last item is the sum of the whole list. Ints stay ints, floats stay floats, as with +.

Examples

print(vec.cumsum([1, 2, 3, 4]))print(vec.cumsum([0.5, 0.25, 0.25]))print(vec.cumsum([1, -3, 2]))

[1, 3, 6, 10][0.5, 0.75, 1.0][1, -2, 0]

Edge cases

• The empty list, or null, gives the empty list; one item gives itself.
• The totals are plain float additions, so they carry float rounding: [0.1, 0.2, 0.3] sums to 0.6000000000000001, unlike sum, which is compensated.
• A mixed list turns to floats from the first float on.

print(vec.cumsum([]), vec.cumsum(null), vec.cumsum([7]))print(vec.cumsum([0.1, 0.2, 0.3]))print(vec.cumsum([1, 0.5, 2]))

[] [] [7][0.1, 0.30000000000000004, 0.6000000000000001][1, 1.5, 3.5]

Errors

An item that is not an int or a float, or an argument that is not a list, is a runtime error, not an error value. A total past 64 bits is an integer overflow runtime error.

print(vec.cumsum([1, "a"]))

line 1: `vec.cumsum` expects numbers, got int and str

print(vec.cumsum([9223372036854775807, 1]))

line 1: integer overflow

Chaining

A list of daily sales piped through vec.cumsum is the running total to each day:

let sales = [3, 5, 4, 6, 8]print(sales | vec.cumsum)print(sales | vec.cumsum | last)

[3, 8, 12, 18, 26]26

See also

vec.cumprod, vec.diff, sum, vec.rolling_sum

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