R: Reverse Cumulative Sum

revcumsum {spatstat.utils} | R Documentation

## Reverse Cumulative Sum

### Description

Returns a vector of cumulative sums of the input values, running in reverse order. That is, the `i`th entry in the output is the sum of entries `i` to `n` in the input, where `n` is the length of the input.

### Usage

    revcumsum(x)

### Arguments

`x` | A numeric or complex vector.

### Details

This low-level utility function is a faster alternative to `rev(cumsum(rev(x)))` under certain conditions. It computes the reverse cumulative sum of the entries of `x`. If `y <- revcumsum(x)`, then `y[i] = sum(x[i:n])` where `n = length(x)`.

This function should not be used if `x` could contain `NA` values: this would lead to an error.

### Value

A vector of the same length and type as `x`.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au.

### See Also

`cumsum`.

### Examples

      revcumsum(1:5)
      rev(cumsum(rev(1:5)))
      x <- runif(1e6)
      system.time(rev(cumsum(rev(x))))
      system.time(revcumsum(x))

[Package spatstat.utils version 2.3-1 Index]