Question

I’m trying to create 4 new variables from a dataset in R that contains a varying number of observations for each identifier (ID). I want to summarize this information into 2 flags that indicate whether an ID has an observation of type A or B and 2 counter variables containing the total number of A’s and B’s per ID.

ID<-c(1,1,1,1,1,1,1,2,2,2,2,2,2)
Result<-c('A','A','B','A','A','A','A','B','B','B','B','B','B')
DSN<-data.frame(ID,Result)

The output would be:

    ID  A_Flag  B_Flag  A_Count B_Count
    1   Y   Y   6   1
    2   N   Y   0   6

Answer 1

Probably the easiest is to use xtabs:

> xtabs(~ID+Result, DSN)
   Result
ID  A B
  1 6 1
  2 0 6

Obviously a flag can be trivially derived from the above:

> xtabs(~ID+Result, DSN) > 0
   Result
ID      A    B
  1  TRUE TRUE
  2 FALSE TRUE