Tidyverse: Reduce variables by group

Question

I have a data frame that looks like this:

ID  pick1      pick2     pick3
1   NA         21/11/29  21/11/30
2   21/11/28   21/11/29  NA
3   21/11/28   NA        21/11/30   
4   NA         21/11/29  21/11/30

Each participant (ID) could pick 2 dates out of 3 options. Now I want to summarize the selected dates to get a tibble like this:

ID  date1      date2
1   21/11/29   21/11/30
2   21/11/28   21/11/29
3   21/11/28   21/11/30   
4   21/11/29   21/11/30

However, I can't get it working using tidyverse functions only. I have started to use this library but couldn't find a solution for my issue online

Answer 1

One option is with rowwise - group by rows, do the sort with na.last as TRUE, keep the sorted output in a list, unnest to multiple columns, and select only columns having at least one non-NA elements

library(dplyr)
library(tidyr)
library(stringr)
 df1 %>% 
   rowwise %>% 
   transmute(ID, date = list(sort(c_across(starts_with('pick')), 
       na.last = TRUE))) %>% 
   ungroup %>%
   unnest_wider(date) %>%
   rename_with(~ str_c('date', seq_along(.)), -ID) %>%
   select(where(~ any(!is.na(.))))

-output

# A tibble: 4 × 3
     ID date1    date2   
  <int> <chr>    <chr>   
1     1 21/11/29 21/11/30
2     2 21/11/28 21/11/29
3     3 21/11/28 21/11/30
4     4 21/11/29 21/11/30

---

or reshape to 'long' format with pivot_longer remove the NAs and reshape it back to 'wide' format

library(stringr)
df1 %>% 
   pivot_longer(cols = -ID, values_drop_na = TRUE) %>%
   group_by(ID) %>% 
   mutate(name = str_c('date', row_number())) %>%
   ungroup %>% 
   pivot_wider(names_from = name, values_from = value)

-output

# A tibble: 4 × 3
     ID date1    date2   
  <int> <chr>    <chr>   
1     1 21/11/29 21/11/30
2     2 21/11/28 21/11/29
3     3 21/11/28 21/11/30
4     4 21/11/29 21/11/30

data

df1 <- structure(list(ID = 1:4, pick1 = c(NA, "21/11/28", "21/11/28", 
NA), pick2 = c("21/11/29", "21/11/29", NA, "21/11/29"), pick3 = c("21/11/30", 
NA, "21/11/30", "21/11/30")), class = "data.frame",
 row.names = c(NA, 
-4L))