rdplyrgroupmutate

find the first TRUE within a group

I want to save the position of the first TRUE in level variable within each id. I am doing the below:

library(tidyverse)

data <- data %>%
  group_by(id) %>%
  mutate(first_true = min(which(data$level == TRUE))) %>%
  ungroup()

However, the result for first_true is the same for all id. group_by(id) is not working. Any idea of what might be happening?

Example data:

id <- c(1,1,1,2,2,2,3,3,3)
level <- c(FALSE,FALSE,FALSE,FALSE,TRUE,TRUE,TRUE,TRUE,TRUE)
data <- data.frame(id, level)
data$level <- as.logical(data$level)

I would like to obtain:

id level
1 0
1 0
1 0
2 2
2 2
2 2 
3 1
3 1
3 1
Solution

  • You can try

    data %>%
    mutate(first_true = ifelse(any(level), min(which(level)), 0), .by = id)

    which gives

      id level first_true
1  1 FALSE          0
2  1 FALSE          0
3  1 FALSE          0
4  2 FALSE          2
5  2  TRUE          2
6  2  TRUE          2
7  3  TRUE          1
8  3  TRUE          1
9  3  TRUE          1