[R] assign index to colnames(matrix)

[Prew, Paul]

Jim, thank you, that worked great.

Paul Prew  |  Statistician
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-----Original Message-----
From: Jim Lemon [mailto:jim at bitwrit.com.au] 
Sent: Friday, February 22, 2013 7:22 PM
To: Prew, Paul
Cc: r-help at r-project.org
Subject: Re: [R] assign index to colnames(matrix)

On 02/23/2013 11:34 AM, Prew, Paul wrote:
> Hello,  I’m trying to follow the syntax of a script from a journal 
> website.  In order to create a regression formula used later in the 
> script, the regression matrix must have column names “X1”, 
> “X2”, etc.  I have tried to assign these column names to my matrix 
> ScoutRSM.mat using a for loop, but I don’t know how to interpret the 
> error message.  Suggestions?  Thanks, Paul
>
>
> ====================================================
> ====== instructions about dimnames(X)[[2]] = "X1","X2",...  ======= 
> ====================================================
>
> function(binstr)
> {
>    # makes formula for regression
>    # must make sure dimnames(X)[[2]] = "X1","X2",...
>    ind<-which(binstr==1)
>    rht<- paste("X", ind, sep="", collapse="+")
>    ans<-paste("y ~ ", rht)
>    return(as.formula(ans))
> }
>
>
> #######################################
> ##############  my for loop  ############## 
> #######################################
>
> for (i in 1:dim(ScoutRSM.mat)[2]  {
> colnames(ScoutRSM.mat)[i]<- paste("X", i, sep = “”)) }
>
>> for(i in 1:dim(ScoutRSM.mat)[2]) {
> +   colnames(ScoutRSM.mat)[i]<- paste("X",i, sep = "") }
> Error in `colnames<-`(`*tmp*`, value = "X1") :
>    length of 'dimnames' [2] not equal to array extent
>
Hi Paul,
You don't really need the loop, try:

colnames(ScoutRSM.mat)<-paste("X",1:dim(ScoutRSM.mat)[2],sep="")

Jim

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