Re: [R] iterating over groups of columns

From: Jannis <bt_jannis_at_yahoo.de>
Date: Tue, 08 Jun 2010 23:08:26 +0200

you should have found a solution for that in the help page of apply.

just run

min.values = apply(the.data,1,min)

the '1' marks the direction (e.g. whether apply is applied to rows or columns), it could be a 2 as well. Check that yourself in the apply documentation.

Then run rbind(the.data,min.values) (could be cbind as well, I am not sure again ;-) ) and you get what you want.

09wkj schrieb:
> I am mainly a Java/C++ programmer, so my mind is used to iterating over data with for loops. After a long break, I am trying to get back into the "R mindset", but I could not find a solution in the documentation for the applys, aggregate, or by.
>
> I have a data.frame where each row is an entry with 10 groups of measurements. The first measurement spans 1 column, the second spans 2 columns, third 3, and so on (55 total columns). What I want to do is add to my data.frame 10 new columns containing the minimum value of each measurement.
>
> dim(the.data)
> [1] 1679 55
>
>
>> colnames(the.data)
>>
> [1] "k.1.1" "k.2.1" "k.2.2" "k.3.1" "k.3.2" "k.3.3" "k.4.1"
> [8] "k.4.2" "k.4.3" "k.4.4" "k.5.1" "k.5.2" "k.5.3" "k.5.4"
> [15] "k.5.5" "k.6.1" "k.6.2" "k.6.3" "k.6.4" "k.6.5" "k.6.6"
> [22] "k.7.1" "k.7.2" "k.7.3" "k.7.4" "k.7.5" "k.7.6" "k.7.7"
> [29] "k.8.1" "k.8.2" "k.8.3" "k.8.4" "k.8.5" "k.8.6" "k.8.7"
> [36] "k.8.8" "k.9.1" "k.9.2" "k.9.3" "k.9.4" "k.9.5" "k.9.6"
> [43] "k.9.7" "k.9.8" "k.9.9" "k.10.1" "k.10.2" "k.10.3" "k.10.4"
> [50] "k.10.5" "k.10.6" "k.10.7" "k.10.8" "k.10.9" "k.10.10"
>
> I want to add to the.data new columns: min.k.1, min.k.2, ..., min.k.10
>
> This is the section of code I would like to improve, hopefully getting rid of the eval and the for loop:
>
> for(k in 1:10){
> s <- subset(the.data, select=paste("k", k, 1:k, sep="."))
> eval(parse(text = paste("the.data$min.k.", k, "<-as.vector(by(s, 1:nrow(s), min))", sep="")))
> }
>
> Thanks for any help,
> Bill
> ______________________________________________
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>



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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. Received on Tue 08 Jun 2010 - 21:11:01 GMT

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