Question

How can I convert the data.frame below to a matrix as given? the first two columns of the data.frame contain the row variables, all combinations of the other columns (except the one containing the values) determine the columns. Ideally, I’m looking for a solution that does not require further packages (so no reshape2 solution). Also, no ftable solution.

(df <- data.frame(c1=rep(c(1, 2), each=8), c2=rep(c(1, 2, 1, 2), each=4),
                  gr=rep(c(1, 2), 8), subgr=rep(c(1,2), 4, each=2), val=1:16) )

c1 c2 gr1.subgr1 gr1.subgr2 gr2.subgr1 gr2.subgr2
1  1   1          3          2          4
1  2   5          7          6          8
2  1   9         11         10         12
2  2  13         15         14         16

Answer 1

Use an interaction variable to construct the groups:

newdf <- reshape(df, idvar=1:2, direction="wide", 
            timevar=interaction(df$gr,df$subgr) , 
            v.names="val", 
            drop=c("gr","subgr") ) 
names(newdf)[3:6] <- c("gr1.subgr1", "gr1.subgr2", "gr2.subgr1",  "gr2.subgr2")
 newdf
   c1 c2 gr1.subgr1 gr1.subgr2 gr2.subgr1 gr2.subgr2
1   1  1          1          2          3          4
5   1  2          5          6          7          8
9   2  1          9         10         11         12
13  2  2         13         14         15         16