[R] selecting rows based on multiple criteria

[Enrico R. Crema]

Dear List, 

I am struggling with the following problem. 

Suppose I have the following data.frame:

coord<-expand.grid(x=1:10,y=1:10)

and I want to extract the row numbers of those matching the criteria defined by the following data.frame:

choice<-data.frame(x=c(2,1,2),y=c(1,2,2))

the result should return in this case:

2,11,12

All I managed to do is the following:

which(data coord$x%in%choice$x & coord$y%in%choice$y);

which returns c(1,2,11,12)... which includes also the first row... 

Any thoughts?

Enrico