[R] cross-product

[Marc Schwartz]

On Dec 17, 2009, at 9:47 AM, Chuck White wrote:

> Hello -- I am trying to create a dataframe whose rows are the cross  
> product of rows in two other dataframes. Here's an example:
>
> A = data.frame(F1=c('1','2','3','2'))
> B = data.frame(F2=c('4','5'))
> C = data.frame()
> for (x in unique(A[,'F1'])) {
>    C = rbind(C, cbind(F1=x,B))
> }
>
> How can I achieve this without the for loop?  Thanks.



See ?merge

 > merge(unique(A), B)
   F1 F2
1  1  4
2  2  4
3  3  4
4  1  5
5  2  5
6  3  5


BTW, avoid using 'C' as the name of an object, as C() is a function in  
R. R will typically know the difference, but it is a good defensive  
programming habit to avoid assigning objects to pre-existing function  
names.

HTH,

Marc Schwartz