Multiply a data frame row-by-row

Question

Input file:

df1 <- data.frame(row.names=c(\"w\",\"x\",\"y\",\"z\"), 
                  A=c(0,0,0,0),
                  B=c(0,1,0,0), 
                  C=c(1,         


        

Answer 1

dat <- read.table(textConnection("  A B C D
+ w 0 0 1 1
+ x 0 1 0 1
+ y 0 0 1 1
+ z 0 0 0 1
+ "), header=TRUE)
> combos <- combn(rn,2)
> combos
     [,1] [,2] [,3] [,4] [,5] [,6]
[1,] "w"  "w"  "w"  "x"  "x"  "y" 
[2,] "x"  "y"  "z"  "y"  "z"  "z" 

apply(combos,2, function(x) c(x[1], x[2], unlist(dat[x[1],]*dat[x[2],])))
  [,1] [,2] [,3] [,4] [,5] [,6]
  "w"  "w"  "w"  "x"  "x"  "y" 
  "x"  "y"  "z"  "y"  "z"  "z" 
A "0"  "0"  "0"  "0"  "0"  "0" 
B "0"  "0"  "0"  "0"  "0"  "0" 
C "0"  "1"  "0"  "0"  "0"  "0" 
D "1"  "1"  "1"  "1"  "1"  "1" 

So the final solution:

t( apply(combos,2, function(x) c(x[1], x[2], unlist(dat[x[1],]*dat[x[2],]))) )

If you convert the combos to a dataframe you would also be able to cbindmatrix as type "numeric":

 cbind( as.data.frame(t(combos)), 
        t( apply(combos,2, function(x)  
                    unlist(dat[x[1],]*dat[x[2],]))) )

  V1 V2 A B C D
1  w  x 0 0 0 1
2  w  y 0 0 1 1
3  w  z 0 0 0 1
4  x  y 0 0 0 1
5  x  z 0 0 0 1
6  y  z 0 0 0 1