R: 'Multiply' dataframe columns of strings

Question

Not sure what this operation is called, and Google did not help.

Say I have two simple dataframes like this:

df1 <- data.frame(factor1 = c(\"a\", \"b         


        

Answer 1

Here is another option with expand.grid

Map(expand.grid, factor1 = df1, factor2 = df2)$factor
#    factor1 factor2
#1       a       x
#2       b       x
#3       c       x
#4       a       y
#5       b       y
#6       c       y
#7       a       z
#8       b       z
#9       c       z

Answer 2

It's a cartesian product of the two data frames, when there's no common names, you can use merge:

merge(df1, df2)   

#  factor1 factor2
#1       a       x
#2       b       x
#3       c       x
#4       a       y
#5       b       y
#6       c       y
#7       a       z
#8       b       z
#9       c       z

Or more explicitly:

merge(df1, df2, by=c())

According to ?merge, when there are no columns to join by, it returns a cartesian product of the two data frames:

If by or both by.x and by.y are of length 0 (a length zero vector or NULL), the result, r, is the Cartesian product of x and y, i.e., dim(r) = c(nrow(x)*nrow(y), ncol(x) + ncol(y)).