'Stretch' a grouped data frame using dplyr

September 5, 2022

I have a grouped dataframe with multiple IDs with a date and value column.

id <- c("a", "a", "a", "b", "b", "b", "c")
date <- c("2020-01-01", "2020-01-02", "2020-01-03",
          "2020-01-01", "2020-01-02", "2020-01-03",
          "2020-01-01")
value <- rnorm(n = length(id))
df <- cbind.data.frame(id, date, value)

However, some IDs have less than 3 dates. I want to "stretch" those IDs and add an NA for the value column for the new dates. In this dataframe, the "c" ID would have two new dates added ("2020-01-02" and "2020-01-03").

>Solution :

Perhaps this approach would suit?

library(tidyverse)

id <- c("a", "a", "a", "b", "b", "b", "c")
date <- c("2020-01-01", "2020-01-02", "2020-01-03",
          "2020-01-01", "2020-01-02", "2020-01-03",
          "2020-01-01")
value <- rnorm(n = length(id))
df <- cbind.data.frame(id, date, value)

df %>%
  right_join(df %>% expand(id, date))
#> Joining, by = c("id", "date")
#>   id       date      value
#> 1  a 2020-01-01 -1.5371474
#> 2  a 2020-01-02  0.9001098
#> 3  a 2020-01-03  0.1523491
#> 4  b 2020-01-01  0.8194577
#> 5  b 2020-01-02  1.2005270
#> 6  b 2020-01-03  0.1158812
#> 7  c 2020-01-01 -0.8676445
#> 8  c 2020-01-02         NA
#> 9  c 2020-01-03         NA

^{Created on 2022-09-05 by the reprex package (v2.0.1)}