CODEWITHSUNDEEP
rdplyr
Alex Gold
Alex Gold

Reputation: 355

Fill column with prior nonmissing value, no ID

I'm trying to fill a missing ID column of a data frame as shown below. It's not blank in the first row it applies to and then blank until the next ID. I wrote ugly code to do this in a for loop, but wonder if there's a tidy-ier way to do this. Any suggestions?

Here's what I've got:

   code data
1     A    1
2          2
3          3
4          4
5          5
6          6
7          7
8          8
9          9
10        10
11    B   11
12        12
13        13
14        14
15        15
16    C   16
17        17
18        18
19        19
20        20

I want: 

   code data
1     A    1
2     A    2
3     A    3
4     A    4
5     A    5
6     A    6
7     A    7
8     A    8
9     A    9
10    A   10
11    B   11
12    B   12
13    B   13
14    B   14
15    B   15
16    C   16
17    C   17
18    C   18
19    C   19
20    C   20

Code I've got now:

# Create mock data frame
df <- data.frame(code = c("A", rep("", 9), 
                          "B", rep("", 4), 
                          "C", rep("", 4)), 
                 data = 1:20)

# For loop over rows (BAD!)
for (i in seq(2, nrow(df))) {
  df[i,]$code <- ifelse(df[i,]$code == "", df[i-1,]$code, df[i, ]$code)
}

Upvotes: 1

Views: 33

Answers (1)

Kerry Jackson
Kerry Jackson

Reputation: 1871

There is a tidyr way to do it, there is the fill function. You also need to replace the zero length string with NA for this to work, which you can easily do using the mutate and na_if functions from dplyr.

df %>% 
  mutate(code = na_if(code,"")) %>% 
  fill(code)

   code data
1     A    1
2     A    2
3     A    3
4     A    4
5     A    5
6     A    6
7     A    7
8     A    8
9     A    9
10    A   10
11    B   11
12    B   12
13    B   13
14    B   14
15    B   15
16    C   16
17    C   17
18    C   18
19    C   19
20    C   20

Upvotes: 2

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