Rowwise cumulative sum
I have a data.table
dt
as follows.
df <- data.frame(t1 = rep(0,5), t3 = c(12, 5, 8,9, 5), t7= c(25, 48, 7, 9, 14))
dt <- setDT(df)
dt
t1 t3 t7
1: 0 12 25
2: 0 5 48
3: 0 8 7
4: 0 9 9
5: 0 5 14
I want to get the cumulative sums across the columns. I am only getting it across the rows. How to do this in data.table
.
dt[, 1:3 := cumsum(dt)]
dt
t1 t3 t7
1: 0 12 25
2: 0 17 73
3: 0 25 80
4: 0 34 89
5: 0 39 103
The desired output is as follows:
dt
t1 t3 t7
1: 0 12 37
2: 0 5 53
3: 0 8 15
4: 0 9 18
5: 0 5 19
Solution 1:
Another option use Reduce
with accumulate=TRUE
:
dt[, names(dt) := Reduce(`+`, dt, accumulate = TRUE)]
dt
# t1 t3 t7
#1: 0 12 37
#2: 0 5 53
#3: 0 8 15
#4: 0 9 18
#5: 0 5 19
Solution 2:
If we need to do this by row, then one option is group by row, unlist
, get the cumsum
, convert to list
and assign it to the columns
dt[, (1:3) := as.list(cumsum(unlist(.SD))), 1:nrow(dt)]
dt
# t1 t3 t7
#1: 0 12 37
#2: 0 5 53
#3: 0 8 15
#4: 0 9 18
#5: 0 5 19
Or another option is rowCumsums
from matrixStats
, which can be applied to a matrix
library(matrixStats)
dt[, (1:3) := as.data.table(rowCumsums(as.matrix(.SD)))]