Replace with 0 the first calculation in mutate and rollapply in R

Question

i have a data frame in R called Data.

library(tibble)
library(dplyr)
library(zoo)
Data <- tibble(
  var = c("A", "A", "A", "A", "A","A"),
  val = c(1, 1, 1, 1, 1.5 , 1.5)
)%>%
  mutate( roll_sd   = rollapplyr(val, width = seq_len(n()), FUN = function(x) sd(x, na.rm = TRUE), fill = NA))
Data

with output :

# A tibble: 6 × 3
  var     val roll_sd
  <chr> <dbl>   <dbl>
1 A       1    NA    
2 A       1     0    
3 A       1     0    
4 A       1     0    
5 A       1.5   0.224
6 A       1.5   0.258

i want the first roll_sd other than 0 to be again 0 and then to continue as it is originally calculated. How can i do it in R ?

Ideally the outpout i want to be like this :

# A tibble: 6 × 3
  var     val roll_sd
  <chr> <dbl>   <dbl>
1 A       1    NA    
2 A       1     0    
3 A       1     0    
4 A       1     0    
5 A       1.5   0
6 A       1.5   0.258

Answer 1

Depending on what your answer is to my comment, I believe something like this may work for you:

library(tibble)
library(dplyr)
library(zoo)

Data <- tibble(
  var = c("A", "A", "A", "A", "A","A"),
  val = c(1, 1, 1, 1, 1.5 , 1.5)
)%>%
  mutate( roll_sd   = rollapplyr(val, width = seq_len(n()), 
                                 FUN = function(x) sd(x, na.rm = TRUE), 
                                 fill = NA))

Data <- rbind(Data, Data) # added so there are 2 places to be set to 0

to_zero <- which(!is.na(Data$roll_sd) & Data$roll_sd > 0) # find all non-0 and non-NA numbers
non_consecutive <- to_zero[c(TRUE, diff(to_zero) > 1)] # get every "first" non-0 number
Data$roll_sd[non_consecutive] <- 0 # set to 0

> Data

# A tibble: 12 × 3
   var     val roll_sd
   <chr> <dbl>   <dbl>
 1 A       1    NA    
 2 A       1     0    
 3 A       1     0    
 4 A       1     0    
 5 A       1.5   0    
 6 A       1.5   0.258
 7 A       1    NA    
 8 A       1     0    
 9 A       1     0    
10 A       1     0    
11 A       1.5   0    
12 A       1.5   0.258