revcumsum | R Documentation |
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.
revcumsum(x)
x |
A numeric or complex vector. |
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.
A vector of the same length and type as x
.
.
cumsum
.
revcumsum(1:5)
rev(cumsum(rev(1:5)))
x <- runif(1e6)
system.time(rev(cumsum(rev(x))))
system.time(revcumsum(x))
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