[R] Indexing Elements of a Dataframe

[John Fox]

Dear Wolfgang,

I'm not sure exactly what you want to do, or why the result needs to be a 
data frame, but what about something like the following?

     > rows <- c(10, 20, 30)
     > cols <- c(200, 400, 600)
     > df <- as.data.frame(outer(rows, cols, function(r, c) r + c))
     > row.names(df) <- letters[1:3]
     > names(df) <- LETTERS[1:3]
     > df
         A   B   C
     a 210 410 610
     b 220 420 620
     c 230 430 630

Or perhaps you want the elements of rows and cols as row and column names:

     > row.names(df) <- rows
     > names(df) <- cols
     > df
        200 400 600
     10 210 410 610
     20 220 420 620
     30 230 430 630

Of course, you'd replace the function argument to outer with an appropriate 
function.


I hope that this helps,
  John

At 01:40 PM 5/28/2002 -0500, Wolfgang Viechtbauer wrote:

>Let's say that I have the following code:
>
>for (i in c(10, 20, 30)) {
>   for (j in c(200, 400, 600)) {
>     ...
>     ...
>     x <- "something"
>     * (code here)
>   }
>}
>
>* Now, x is some result that I want to put into a results "matrix" that
>looks like this:
>
>    200 400 600
>10
>20
>30
>
>I came up with an ad-hoc solution adding some counters (called "ro" and
>"co") and using a matrix for the results, which I could index with those
>counters (results[ro,co] <- x) and then converting that matrix into a
>dataframe and changing the row and column names. That seems a little too
>convoluted.
>
>I tried to come up with a "neater" solution, trying to create a
>dataframe that looks like the one above and then indexing the fields in
>the dataframe by results$i[j] but I couldn't get it to work. Is there a
>way of doing this or maybe a better solution?

-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox
-----------------------------------------------------

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