r - Fill missing dates by group

Question

In my data, there exist observations for some IDs in some months and not for others, e.g.

dat <- data.frame(c(1, 1, 1, 2, 3, 3, 3, 4, 4, 4), c(rep(30, 2), rep(25, 5), rep(20, 3)), c('2017-01-01', '2017-02-01', '2017-04-01', '2017-02-01', '2017-01-01', '2017-02-01', '2017-03-01', '2017-01-01',
                    '2017-02-01', '2017-04-01'))
colnames(dat) <- c('id', 'value', 'date')

I would like to, for each id value, insert a row that includes the month(s) missing for that id and NA for value.

Is there a way to (somewhat) concisely do this for all months in seq(min(as.Date(dat$date)), max(as.Date(dat$date)), by = 'months')? I often use tidyverse and data.table, but am open to any approach.

Answer 1

tidyr::complete() fills missing values

add id and date as the columns (...) to expand for

library(tidyverse)

complete(dat, id, date)


# A tibble: 16 x 3
      id date       value
   <dbl> <date>     <dbl>
 1  1.00 2017-01-01  30.0
 2  1.00 2017-02-01  30.0
 3  1.00 2017-03-01  NA  
 4  1.00 2017-04-01  25.0
 5  2.00 2017-01-01  NA  
 6  2.00 2017-02-01  25.0
 7  2.00 2017-03-01  NA  
 8  2.00 2017-04-01  NA  
 9  3.00 2017-01-01  25.0
10  3.00 2017-02-01  25.0
11  3.00 2017-03-01  25.0
12  3.00 2017-04-01  NA  
13  4.00 2017-01-01  20.0
14  4.00 2017-02-01  20.0
15  4.00 2017-03-01  NA  
16  4.00 2017-04-01  20.0