How to concatenate character strings based on condition in r?

I need to prepare queries that are made of characters strings (DOI, Digital Object Identifier) stored in a data frame. All strings associated with the same case have to be joined to produce one query.

The df looks like this:

Case	DOI
1	1212313/dfsjk23
1	322332/jdkdsa12
2	21323/xsw.w3
2	311331313/q1231
2	1212121/1231312

The output should be a data frame looking like this:

Case	Query
1	DO=(1212313/dfsjk23 OR 322332/jdkdsa12)
2	DO=(21323/xsw.w3 OR 311331313/q1231 OR 1212121/1231312)

The prefix ("DO="), suffix (")") and "OR" are not critical, I can add them later, but how to aggregate character strings based on a case number?

Solution

In base R you could do:

aggregate(DOI~Case, df1, function(x) sprintf('DO=(%s)', paste0(x, collapse = ' OR ')))
  Case                                                     DOI
1    1                 DO=(1212313/dfsjk23 OR 322332/jdkdsa12)
2    2 DO=(21323/xsw.w3 OR 311331313/q1231 OR 1212121/1231312)

if Using R 4.1.0

aggregate(DOI~Case, df1, \(x)sprintf('DO=(%s)', paste0(x, collapse = ' OR ')))