How do you merge tables by ID, then combine cells with the same ID

Question

Table1:

      ID Sex
1: 12345   M
2: 23456   M
3: 34567   F
4: 45678   F
5: 56789   F

Table2:

      ID  name
1: 12345   sam
2: 23456  jack
3: 23456   tom
4: 56789 steve
5: 56789   rob

I need to merge these two tables to get:

   ID Sex      name
1: 12345   M       sam
2: 23456   M  jack,tom
3: 34567   F          
4: 45678   F          
5: 56789   F steve,rob

I tried to use the Join function but it doesn't allow me to combine those names, is there a good way to solve this?

Answer 1

If these are data.tables, one option would be to paste the 'name' by 'ID' in the second dataset 'dt2' and join with the first ('dt1') on 'ID' and create the column 'name' in the first dataset

library(data.table)
dt1[dt2[, .(name = toString(name)), ID], name := name, on = .(ID)]
dt1
#      ID Sex       name
#1: 12345   M        sam
#2: 23456   M  jack, tom
#3: 34567   F       <NA>
#4: 45678   F       <NA>
#5: 56789   F steve, rob

Answer 2

This is a combination of three separate operations that have been covered in detail in other answers on this site:

1. You want to join the tables together :

   • How to join (merge) data frames (inner, outer, left, right)?

2. then spread from long to wide format

   • How to reshape data from long to wide format?

3. and finally paste those multiple 'name' columns together into a single name column

   • How to combine two or more columns in a dataframe into a new column with a new name?