R: Set next row to NA in group_by - r

Question

I want to set the next row i+1 in the same column to NA if there is already an NA in row i and then do this by groups. Here is my attempt:
dfeg <- tibble(id = c(rep("A", 5), rep("B", 5)),
x = c(1, 2, NA, NA, 3, 5, 6, NA, NA, 7))
setNextrowtoNA <- function(x){
for (j in 1:length(x)){
if(is.na(x[j])){x[j+1] <- NA}
}
}
dfeg <- dfeg %>% group_by(id) %>% mutate(y = setNextrowtoNA(x))
However my attempt doesn't create the column y that am looking for. Can anyone help with this? Thanks!
EDIT: In my actual data I have multiple values in a row that need to be set to NA, for example my data is more like this:
dfeg <- tibble(id = c(rep("A", 6), rep("B", 6)),
x = c(1, 2, NA, NA, 3, 4, 15, 16, NA, NA, 17, 18))
And need to create a column like this:
y = c(1, 2, NA, NA, NA, NA, 15, 16, NA, NA, NA, NA)
Any ideas? Thanks!
EDIT 2:
I figured it out on my own, this seems to work:
dfeg <- tibble(id = c(rep("A", 6), rep("B", 6)),
x = c(1, 2, NA, NA, 3, 4, 15, 16, NA, NA, 17, 18))
setNextrowtoNA <- function(x){
for (j in 1:(length(x))){
if(is.na(x[j]))
{
x[j+1] <- NA
}
lengthofx <- length(x)
x <- x[-lengthofx]
print(x[j])
}
return(x)
}
dfeg <- dfeg %>% group_by(id) %>% mutate(y = NA,
y = setNextrowtoNA(x))

Answer 1

Use cumany:
library(dplyr)
dfeg %>%
group_by(id) %>%
mutate(y = ifelse(cumany(is.na(x)), NA, x))
id x y
<chr> <dbl> <dbl>
1 A 1 1
2 A 2 2
3 A NA NA
4 A NA NA
5 A 3 NA
6 A 4 NA
7 B 15 15
8 B 16 16
9 B NA NA
10 B NA NA
11 B 17 NA
12 B 18 NA
Previous answer:
Use an ifelse statement with lag:
library(dplyr)
dfeg %>%
group_by(id) %>%
mutate(y = ifelse(is.na(lag(x, default = 0)), NA, x))