frollapply can produce output longer than the input when the window-length is also longer than the input

[hadley-johnson]

Is it expected that the new version of frollapply() and frollsum() for data.table version 1.18 behave differently when the window length is larger than the data object? Or is this a bug?

The difference noted below does not happen using data.table version 1.17.

Using frollsum() the output always has the same length as the input object:

frollsum(c(1,2,3,4,5),n=5)
[1] NA NA NA NA 15
frollsum(c(1,2,3,4,5),n=6)
[1] NA NA NA NA NA
frollsum(c(1,2,3,4,5),n=7)
[1] NA NA NA NA NA

But using frollapply() the output can be longer than the input object:

frollapply(c(1,2,3,4,5),N=5,FUN=sum)
[1] NA NA NA NA  15
frollapply(c(1,2,3,4,5),N=6,FUN=sum)
[1] NA NA NA NA NA
frollapply(c(1,2,3,4,5),N=7,FUN=sum)
[1] NA NA NA NA NA NA

[r2evans]

This is a change in behavior.

library(data.table)
packageVersion("data.table")
# [1] ‘1.17.8’

frollsum(c(1,2,3,4,5),n=5)
# [1] NA NA NA NA 15
frollsum(c(1,2,3,4,5),n=7)
# [1] NA NA NA NA NA
frollapply(c(1,2,3,4,5),n=5,FUN=sum)
# [1] NA NA NA NA 15
frollapply(c(1,2,3,4,5),n=7,FUN=sum)
# [1] NA NA NA NA NA

and

library(data.table)
packageVersion("data.table")
# [1] ‘1.18.2.1’

frollsum(c(1,2,3,4,5),n=5)
# [1] NA NA NA NA 15
frollsum(c(1,2,3,4,5),n=7)
# [1] NA NA NA NA NA
frollapply(c(1,2,3,4,5),N=5,FUN=sum)
# [1] NA NA NA NA 15
frollapply(c(1,2,3,4,5),N=7,FUN=sum)
# [1] NA NA NA NA NA NA

[jangorecki]

Definitely a bug, thanks for reporting