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rcumsum

Acumulative sum in R

I have data containing columns x and lx, I want to get cumulative sum on lx basis. My data is like:

x l(x)
20 100.000
21 99.644
22 99.286
23 98.925
24 98.561
25 98.195
26 97.829

and I want to get output like :

x l(x)
20 692.440
21 592.440
22 492.796
23 393.510
24 294.585
25 196.024
26 97.829

ie. accumulative sum

So it there a possible way to achieve it?

Solution

  • We can reverse the column, get the cumulative sum (cumsum) and reverse the output

    df$`l(x)` <- with(df, rev(cumsum(rev(`l(x)`))))

    -output

    #  x    l(x)
#1 20 692.440
#2 21 592.440
#3 22 492.796
#4 23 393.510
#5 24 294.585
#6 25 196.024
#7 26  97.829

    Or another option is revcumsum

    library(spatstat.utils)
df$`l(x)` <- revcumsum(df$`l(x)`)

    Or using accumulate from purrr

    library(purrr)
library(dplyr)
df %>%
     mutate(`l(x)` = accumulate(`l(x)`, `+`, .dir = 'backward'))

    data

    df <- structure(list(x = 20:26, `l(x)` = c(100, 99.644, 99.286, 98.925, 
98.561, 98.195, 97.829)), class = "data.frame", row.names = c(NA, 
-7L))