Re: [R] Listing Variables

From: Farrel Buchinsky <fjbuch_at_gmail.com>
Date: Fri 05 May 2006 - 05:44:54 EST

bogdan romocea <br44114 <at> gmail.com> writes:

>
> Here's an example.
> dfr <- data.frame(A1=1:10,A2=21:30,B1=31:40,B2=41:50)
> vars <- colnames(dfr)
> for (v in vars[grep("B",vars)]) print(mean(dfr[,v]))

At first I did not know why you had bothered with the (dfr[,v])) part of the command. I thought you should have just as easily entered ... print(mean(v)). However, with a little help from David Clayton I discovered that one would simply be passing a string to the function rather than the underlying vector whose name is the string. Setting it up as you did makes sure that the vector is passed to the function.

Armed with what I learnt from your response, I reasoned that I could roll everyting into an sapply and get everything coming out as a dataframe meanting that I could do the next step of the analysis. data.frame(sapply(dfr[,grep("B",names(dfr))],mean))

   sapply.dfr...grep..B...names.dfr.....mean.

B1                                       35.5
B2                                       45.5

Farrel Buchinsky



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