CODEWITHSUNDEEP
r
R. Iersel
R. Iersel

Reputation: 109

Mark/Flag last non-zero (or specific) value in a vector

Seemingly simple question yet I can't figure it out nor find the answer. I have the following data:

tibble(A = c(0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0), 
       B = c(1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2))

I now wish to mark/flag (Not extract) the last non-zero value(or the last time A == 1) in a separate column, per group B. Ideally I would like to do so using dplyr:

DF %>% group_by(B) %>%
mutate(C = ???)

I've found lots of answers on how to extract this value, but none on how to flag it. The closest I found was last(A[A==1]), but this sets all C values equally. Instead I only want the last non-zero value per group marked.

My expected output would be something like:

tibble(A = c(0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0), 
       B = c(1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2), 
       C = c(0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0))

Upvotes: 0

Views: 215

Answers (1)

Karthik S
Karthik S

Reputation: 11584

Does this work:

library(dplyr)
df %>% group_by(B) %>% mutate(C = case_when(row_number() == max(which(A == 1)) ~ 1L, TRUE ~ 0L))
# A tibble: 14 x 3
# Groups:   B [2]
       A     B     C
   <dbl> <dbl> <int>
 1     0     1     0
 2     0     1     0
 3     0     1     0
 4     0     1     0
 5     1     1     0
 6     0     1     0
 7     1     1     1
 8     0     2     0
 9     1     2     0
10     1     2     0
11     0     2     0
12     0     2     0
13     1     2     1
14     0     2     0

Upvotes: 3

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