RE: [R] extracting one element of correlation matrices from a list poroduced by the 'by' statement

From: Mohammad A. Chaudhary <mchaudha_at_jhsph.edu>
Date: Thu 14 Apr 2005 - 06:26:45 EST


Great! Thank you very much. Looks R has unlimited possibilities. Regards,
Ashraf

-----Original Message-----
From: pd@pubhealth.ku.dk [mailto:pd@pubhealth.ku.dk] On Behalf Of Peter Dalgaard
Sent: Wednesday, April 13, 2005 4:11 PM
To: Mohammad A. Chaudhary
Cc: r-help@stat.math.ethz.ch
Subject: Re: [R] extracting one element of correlation matrices from a list poroduced by the 'by' statement

"Mohammad A. Chaudhary" <mchaudha@jhsph.edu> writes:

> I am producing 2X2 correlation matrices by a class variable. I need to
> extract a vector of correlation coefficients only. I am doing that in
a
> loop (see below) but I am sure there would be a simpler way. Please
> help!
>
>
>
> > by(d1[,c(2,3)],d1[,1],cor)
>
.....
> c e
>
> c 1.0000000 0.3746597
>
> e 0.3746597 1.0000000
>
> ***********************************************
>
> > t<- rep(0,10)
>
> > ind=0
>
> > for(r in 1:10) {
>
> + ind=ind+1
>
> + t[ind] <- by(d1[,c(2,3)],d1[,1],cor)[[r]][1,2]
>
> + }
>
> > t
>
> [1] 0.1972309 0.2469402 0.3177058 0.3492043 0.3385547 0.2876410
> 0.3374766 0.4380190 0.3452468 0.3746597

One way could be

 sapply(by(d1[2:3],d1[,1],cor),"[",1,2)

another is

 by(d1[2:3],d1[,1],function(f)cor(f)[1,2])

or, (this possibility never occurred to me before)

 by(d1[2:3],d1[,1], with, cor(c,e))

You might want to wrap the last two in a c() construct but they actually are vectors already, they just don't look it when print.by has done its work.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907

______________________________________________
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Received on Thu Apr 14 06:29:03 2005

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:31:08 EST