[R] Creating binary variable depending on strings of two dataframes

[David Winsemius]

On Dec 7, 2010, at 11:30 AM, Pete Pete wrote:

>
> Hi,
> consider the following two dataframes:
> x1=c("232","3454","3455","342","13")
> x2=c("1","1","1","0","0")
> data1=data.frame(x1,x2)
>
> y1=c("232","232","3454","3454","3455","342","13","13","13","13")
> y2=c("E1","F3","F5","E1","E2","H4","F8","G3","E1","H2")
> data2=data.frame(y1,y2)
>
> I need a new column in dataframe data1 (x3), which is either 0 or 1
> depending if the value "E1" in y2 of data2 is true while x1=y1. The  
> result
> of data1 should look like this:
>   x1     x2 x3
> 1 232   1   1
> 2 3454 1   1
> 3 3455 1   0
> 4 342   0   0
> 5 13     0   1
>
> I think a SQL command could help me but I am too inexperienced with  
> it to
> get there.

 > dat3 <- merge(data1, data2[data2$y2=="E1", ], by.x="x1", by.y="y1",  
all.x=TRUE)
 > dat3$y2 <- 0 + (dat3$y2 %in% "E1")
 > dat3
     x1 x2 y2
1   13  0  1
2  232  1  1
3  342  0  0
4 3454  1  1
5 3455  1  0

(Admittedly not in the original order, but in my hands the R merge  
operation doesn't lend itself well to maintaining the original order.  
I see that Grothendieck's solution is better in this respect, a  
typical occurrence in comparison of our respective efforts with R.)

-- 

David Winsemius, MD
West Hartford, CT