Turn vector output into columns in data.table?

Question

I am generating output by applying function to some subsets of data.table. I am using function like this:

data[, foo(args), by=list(Year, Month)]

My function foo return always a vector of length n. I am getting an output like this:

      Year Month           V1
   1: 1983     2 9.734669e-06
   2: 1983     2 9.165665e-06
   3: 1983     2 2.097477e-05
   4: 1983     2 3.803727e-05

But I would like something like

      Year Month           V1           V2           V3           V4 ...
   1: 1983     2 9.734669e-06 9.165665e-06 2.097477e-05 3.803727e-05 ...

I even tried using list(foo(args)), it didn't help. Or should the output be in form foo$V1, foo$V2 ...?

Answer 1

Try

data[, as.list(foo(args)), by=list(Year, Month)] 

or change foo to return a list rather than a vector.