Transposing two fields to one unique key in R [duplicate]

Answer 1

Another option is merged.stack from splitstackshape

 library(splitstackshape)
 res <- merged.stack(DF, var.stubs=c('Name', 'Price'), sep='var.stubs',
                     atStart=FALSE)[,2:= NULL][]
 setnames(res, 2, 'Seller')
 res 
 #    ProductID Seller Price
 #1:         1    A    $1
 #2:         1    X    $3
 #3:         2    B    $3
 #4:         2    Y    $6
 #5:         3    C    $2
 #6:         3    Z    $1