Effective Go Recipes

Recipe 33

Calculating Cumulative Sum

Task

Josh, the ops team lead, asks you to help them with monitoring the server you are developing. He says:

We have a cumSum function that calculates the cumulative sum of a slice of metrics. For example, the cumulative sum of []int{1, 2, 3} is []int{1, 3, 6}. When we use the function, we see that it gets slow on large slices, and the garbage collector starts to work a lot. Can you please have a look and fix it?

You look at the current code to calculate the cumulative sum:

types/slices/cumsum/cumsum.go

// cumSum returns the cumulative sum of values
// cumSum([]int{1, 2, 3}) → []int{1, 3, 6}
func cumSum(values []int) []int {
    var cs []int
    s := 0
    for _, val := range values {
 s += val ...