R dplyr rolling sum

Question

i am implementing a rolling sum calculation through dplyr, but in my database i have a number of variables that have only one or only a few observations, causing an (k is sm

Answer 1

You can instead use RcppRoll::roll_sum which returns NA if the sample size(n) is less than the window size(k).

set.seed(1)
dg$count = rpois(dim(dg)[1], 5) 
library(RcppRoll)
library(dplyr)
dg %>%
     arrange(site,year,animal) %>%
     group_by(site, animal) %>%
     mutate(roll_sum = roll_sum(count, 2, align = "right", fill = NA))    
#       site year animal count roll_sum
#1    Boston 2000    dog     4       NA
#2    Boston 2001    dog     5        9
#3    Boston 2002    dog     3        8
#4    Boston 2003    dog     9       12
#5    Boston 2004    dog     6       15
#6  New York 2000    dog     4       NA
#7  New York 2001    dog     8       12
#8  New York 2002    dog     8       16
#9  New York 2003    dog     6       14
#10 New York 2004    cat     2       NA