[R] R version 3.3.2, Windows 10: Applying a function to each possible pair of rows from two different data-frames

[Rui Barradas]

Hello,

The obvious way would be to preallocate the resulting data.frame, to 
expand an empty one on each iteration being a time expensive operation.

n <- nrow(expand.grid(1:nrow(D1), 1:nrow(D2)))
D4 <- data.frame(distance=integer(n),difference=integer(n))
k <- 0
for (i in 1:nrow(D1)){
	for (j in 1:nrow(D2))  {
		k <- k + 1
		D4[k, ] <- 
c(distance=sqrt(sum((D1[i,1:2]-D2[j,1:2])^2)),difference=(D1[i,3]-D2[j,3])^2)
	}
}

identical(D3, D4)

Hope this helps,

Rui Barradas

Em 23-06-2017 16:19, Rathore, Saubhagya Singh escreveu:
> For certain reason, the content was not visible in the last mail, so posting it again.
>
> Dear Members,
>
> I have two different dataframes with a different number of rows. I need to apply a set of functions to each possible combination of rows with one row coming from 1st dataframe and other from 2nd dataframe. Though I am able to perform this task using for loops, I feel that there must be a more efficient way to do it. An example case is given below. D1 and D2 are two dataframes. I need to evaluate D3 with one column as the Euclidean distance in the x-y plane and second column as squared difference of z values, of each row pair from D1 and D2.
>
> D1<-data.frame(x=1:5,y=6:10,z=rnorm(5))
> D2<-data.frame(x=19:30,y=41:52,z=rnorm(12))
> D3<-data.frame(distance=integer(0),difference=integer(0))
>
> for (i in 1:nrow(D1)){
>
> for (j in 1:nrow(D2))  {
>
> temp<-data.frame(distance=sqrt(sum((D1[i,1:2]-D2[j,1:2])^2)),difference=(D1[i,3]-D2[j,3])^2)
> D3<-rbind(D3,temp)
> }
> }
>
> Thank you
>
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of r-help-owner at r-project.org
> Sent: Friday, June 23, 2017 10:47 AM
> To: Rathore, Saubhagya Singh <saubhagya at gatech.edu>
> Subject: R version 3.3.2, Windows 10: Applying a function to each possible pair of rows from two different data-frames
>
> The message's content type was not explicitly allowed
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>