David Winsemius
On Sep 6, 2008, at 3:00 PM, drflxms wrote:
> Dear R-colleagues,
>
> another question from a newbie: I am creating a lot of simple
> pivot-charts from my raw data using the reshape-package. In these
> charts
> we have medical doctors judging videos in the columns and the videos
> they judge in the rows. Simple example of chart/data.frame "input"
> with
> two categories 1/0:
>
> video 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
>
> 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
> 2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
> 3 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
> 4 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
> 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
> 6 6 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0
> 7 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
> 8 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0
> 9 9 0 0 0 0 0 0 0 0 0 1 0 1 1 0 1 1 0 0 0 1 0
> 10 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
>
> I recently learned, that I can easily create a confusion matrix out of
> this data using the following commands:
>
> pairs<-data.frame(pred=factor(unlist(input[2:21])),ref=factor(input[,
> 22]))
> pred<-pairs$pred
> ref <- pairs$ref
> library (caret)
> confusionMatrix(pred, ref, positive=1)
>
> - where column 21 is the reference/goldstandard.
>
> My problem is now, that I analyse data.frames with an unknown count of
> columns. So to get rid of the first and last column for the "pred"
> variable and to select the last column for the "ref" variable, I
> have to
> look at the data.frame before doing the above commands to set the
> proper
> column numbers.
>
> It would be very comfortable, if I could address the last column not
> by
> number (where I have to count beforehand) but by a variable "last
> column".
>
> Probably there is a more easy solution for this problem using the
> names
> of the columns as well: the reference is always number "21" the first
> column is always called "video". So I tried:
>
> attach(input)
> pairs<-data.frame(pred=factor(unlist(input[[,-c(video,
> 21)]])),ref=factor(input[[21]]))
>
> which does not work unfortunately :-(.
>
> I'd be very happy in case someone could help me out, cause I am really
> tired of counting - there are a lot of tables to analyse...
>
> Cheers and greetings from Munich,
> Felix
>
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