Balance calculation using value of the previous row

Question

Table I have:

DT <- data.frame(A=1:5*10, B=1:5*-1)
DT
   A  B
1 10 -1
2 20 -2
3 30 -3
4 40 -4
5 50 -5

Table I want:

C=A+B+C(n-1)

   A  B  C
1 10 -1  9
2 20 -2 27
3 30 -3 54
4 40 -4 90
5 50 -5 135

I have reference below link and try to apply but fail:

DT$C<-DT$A+DT$B+shift(DT$C)

score 2 · Answer 1 · answered May 10 '16 at 00:19

2

If I am not missing something, this will do the trick:

DT <- data.table(A=1:5*10, B=1:5*-1)
DT[, C := cumsum(A + B)]

answered May 10 '16 at 00:19

Bulat

Good eye! And if it were a dataframe named DF then `DF$C=with(DF, cumsum(A+B))` – IRTFM May 10 '16 at 02:02

score 0 · Answer 2 · answered May 10 '16 at 03:18

0

With dplyr

library(dplyr)
DT %>% 
     mutate(C= cumsum(A+B))
#   A  B   C
#1 10 -1   9
#2 20 -2  27
#3 30 -3  54
#4 40 -4  90
#5 50 -5 135

answered May 10 '16 at 03:18

akrun

2 Answers2