[R] To draw observation [m, n] from 20 data frames named frame1, ... , frame20

[Peter Dalgaard]

Gaurav Ghosh wrote:
> Hi all,
>
> I have 20 data frames, named frame1, ... , frame20.  Each data frame has the
> dimension 20x5.  I need to build a function that calls out the observation in
> Row 1, Col 2 from all 20 data frames and places it in a vector of length 20.  I
> have tried the following code:
>
> vect <- rep(0,20)
> for(i in 1:20){
>     vect[i] <- paste("frame",i,"[1,2]",sep="")
> }
>
> The vector that results is of the form ("frame1[1,2]", ... , "frame20[1,2]"). 
> Instead,  the vector I need has the numerical values that correspond to
> frame1[1,2], frame2[1,2], ... etc.  How should I amend my code?
>
> Thanks,
>
> Gaurav Ghosh
>   
You need an eval(parse(.....)) step if you want to go that route.

However, it is easier if you have your frames in a list to begin with, say

mylist <- mget(sprintf(1:20, fmt="frame%d"))

Then it is just

sapply(mylist, "[", 1, 2)

-- 
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