[R] how to address last and all but last column in dataframe

[drflxms]

Hello Mr. Burns, Hello Mr. Dwinseminus

thank you very much for your incredible quick and efficient reply! I was
completely successful with the following command:

pairs<-data.frame(pred=factor(unlist(input[,-c(1,ncol(input))])),ref=factor(input[,ncol(input)]))

In case of the "input" example data.frame I sent with my question the
above code is equivalent to:
 
pairs<-data.frame(pred=factor(unlist(input[2:17])),ref=factor(input[,18]))

Great! That is exactly what I was looking for! This simple code will
save me hours!

Patrick, your book looks in fact very interesting and will be my perfect
reading material for the following nights :-) (probably not only the
first chapter ;-). Thanks for the hint - and the free book of course.

David, the "input" data.frame is the result of the reshape-command I
performed. I just copied it from the R-console into the e-mail. In fact
the first column "video" is not part of the data, but needed for
analysis with kappam.fleiss function of the irr-package. Sorry, you are
absolutely correct, I should have mentioned this in my question. I will
improve when I ask my next question :-).

Again I like to thank you for your help and wish you a pleasant Sunday.
Greetings from Munich,
Felix

Patrick Burns wrote:
> If I understand properly, you want
>
> input[, -c(1, ncol(input))]
>
> rather than
>
> input[[, -c(video, 21)]]
>
> Chapter 1 of S Poetry might be of interest to you.
>
> Patrick Burns
> patrick at burns-stat.com
> +44 (0)20 8525 0696
> http://www.burns-stat.com
> (home of S Poetry and "A Guide for the Unwilling S User")
>
> 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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>> 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.
>>
>>
>>