R apply function to groups within data frame adding result as additional column - r

Question

Here is the code for my example dataset.
df = data.frame("group" =c(rep(1,5),rep(1,6),rep(2,4),rep(2,3)), "time" = c(rep(NA,5),seq(1,6),rep(NA,4),seq(1,3)), "p" = seq(1,18) )
group time p
1 1 NA 1
2 1 NA 2
3 1 NA 3
4 1 NA 4
5 1 NA 5
6 1 1 6
7 1 2 7
8 1 3 8
9 1 4 9
10 1 5 10
11 1 6 11
12 2 NA 12
13 2 NA 13
14 2 NA 14
15 2 NA 15
16 2 1 16
17 2 2 17
18 2 3 18
I would like to figure out how to apply a function by group to only the values that have time then append the result as a new column in the data frame. Here is my example function I would like to apply.
pfunc <- function(p){
p+5
}
The output I am hoping to obtain would look as follows.
group time p new_p
1 1 NA 1 NA
2 1 NA 2 NA
3 1 NA 3 NA
4 1 NA 4 NA
5 1 NA 5 NA
6 1 1 6 11
7 1 2 7 12
8 1 3 8 13
9 1 4 9 14
10 1 5 10 15
11 1 6 11 16
12 2 NA 12 NA
13 2 NA 13 NA
14 2 NA 14 NA
15 2 NA 15 NA
16 2 1 16 21
17 2 2 17 22
18 2 3 18 23

Answer 1

You can try this:
library(dplyr)
df %>% group_by(group) %>%
mutate(pnew=ifelse(is.na(time),time,time+5))
# A tibble: 18 x 4
# Groups: group [2]
group time p pnew
<dbl> <int> <int> <dbl>
1 1 NA 1 NA
2 1 NA 2 NA
3 1 NA 3 NA
4 1 NA 4 NA
5 1 NA 5 NA
6 1 1 6 6
7 1 2 7 7
8 1 3 8 8
9 1 4 9 9
10 1 5 10 10
11 1 6 11 11
12 2 NA 12 NA
13 2 NA 13 NA
14 2 NA 14 NA
15 2 NA 15 NA
16 2 1 16 6
17 2 2 17 7
18 2 3 18 8
Update
You can use this function:
increase <- function(data,n)
{
data %>% group_by(group) %>%
mutate(pnew=ifelse(is.na(time),time,time+n)) -> result
return(result)
}
increase(df,n = 10)
# A tibble: 18 x 4
# Groups: group [2]
group time p pnew
<dbl> <int> <int> <dbl>
1 1 NA 1 NA
2 1 NA 2 NA
3 1 NA 3 NA
4 1 NA 4 NA
5 1 NA 5 NA
6 1 1 6 11
7 1 2 7 12
8 1 3 8 13
9 1 4 9 14
10 1 5 10 15
11 1 6 11 16
12 2 NA 12 NA
13 2 NA 13 NA
14 2 NA 14 NA
15 2 NA 15 NA
16 2 1 16 11
17 2 2 17 12
18 2 3 18 13
Update 2
I hope this helps:
df %>% group_by(group) %>% rowwise() %>% mutate(pnew=ifelse(is.na(time),NA,pfunc(time)))
# A tibble: 18 x 4
# Rowwise: group
group time p pnew
<dbl> <int> <int> <dbl>
1 1 NA 1 NA
2 1 NA 2 NA
3 1 NA 3 NA
4 1 NA 4 NA
5 1 NA 5 NA
6 1 1 6 6
7 1 2 7 7
8 1 3 8 8
9 1 4 9 9
10 1 5 10 10
11 1 6 11 11
12 2 NA 12 NA
13 2 NA 13 NA
14 2 NA 14 NA
15 2 NA 15 NA
16 2 1 16 6
17 2 2 17 7
18 2 3 18 8