I have a flag column that contains continuous streams 1s and 0s. I want to add the stream of 1s. When it encounters 0s, the summing should stop. For the next stream of 1s, summing should start afresh
I have tried cumsum(negread_flag == 1) this continues to sum after the 0s
negread_flag result
1 1
1 2
1 3
1 4
0 0
0 0
0 0
1 1
1 2
1 3
0 0
We can make use of rleid (run-length-id - to generate different ids when the adjacent element differ) as a grouping variable, then get the sequence of the group and assign it to 'result' where 'negread_flag' is 1, remove the 'grp' column by assigning it to NULL
library(data.table)
setDT(df1)[, grp := rleid(negread_flag)
][, result := 0
][negread_flag == 1,
result := seq_len(.N), grp][, grp := NULL][]
# negread_flag result
# 1: 1 1
# 2: 1 2
# 3: 1 3
# 4: 1 4
# 5: 0 0
# 6: 0 0
# 7: 0 0
# 8: 1 1
# 9: 1 2
#10: 1 3
#11: 0 0
Or a similar idea with tidyverse, using the rleid (from data.table), create the 'result' by multiplying the row_number() with the 'negread_flag' so that values corresponding to 0 in 'negread_flag' becomes 0
library(tidyverse)
df1 %>%
group_by(grp = rleid(negread_flag)) %>%
mutate(result = row_number() * negread_flag) %>%
ungroup %>%
select(-grp)
# A tibble: 11 x 2
# negread_flag result
# <int> <int>
# 1 1 1
# 2 1 2
# 3 1 3
# 4 1 4
# 5 0 0
# 6 0 0
# 7 0 0
# 8 1 1
# 9 1 2
#10 1 3
#11 0 0
Or using base R
i1 <- df1$negread_flag != 0
df1$result[i1] <- with(rle(df1$negread_flag), sequence(lengths * values))
Or as @markus commented
df1$result[i1] <- sequence(rle(df1$negread_flag)$lengths) * df1$negread_flag
df1 <- structure(list(negread_flag = c(1L, 1L, 1L, 1L, 0L, 0L, 0L, 1L,
1L, 1L, 0L)), row.names = c(NA, -11L), class = "data.frame")
