Conditionally swap two columns of a data.frame?

Minter!

Is there an R cookbook? which lists this kind of common problem and
common
solution?


On Thu, 16 Sep 2004, Dimitris Rizopoulos wrote:

Hi Dan,

do you need something like that,

dat <- data.frame(V1=rnorm(40000, 10), V2=rnorm(40000, 10))
ratioV1V2 <- ifelse(dat$V1>dat$V2, dat$V1/dat$V2, dat$V2/dat$V1)

I hope it helps.

Best,
Dimitris

----
Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven

Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/396887
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat/
    http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm

----- Original Message ----- 
From: "Dan Bolser" <dmb at mrc-dunn.cam.ac.uk>
To: <r-help at stat.math.ethz.ch>
Sent: Thursday, September 16, 2004 2:19 PM
Subject: [R] Conditionally swap two columns of a data.frame?

I am doing this a kinda dumb way, and it is apparetnly taking
forever.

I have a data frame with two numeric columns. I want to look at

their

correlation, and I am looking at the size ratio between the two.

i.e.

plot(density(data$V1/data$V2))

This kinda gives me a normal curve showing something about the
distribution of the two values.

I want to make sure that V1/V2 is always > 1 ...

for (i in 1:length(row.names(data)) ){
  ratioV1V2 <- if(V1>V2) V1/V2 else V2/V1
}

This is a bit of a hack, and is taking forever for some reson (about
40,000 rows in my data.frame).

I would just like to swap the values in the data frame (to put the

bigest

first for example), then use the above plot to get what I want.

Should I use the DB backend to the data to make the dump in this

way?

(involves some hacky sql)

Considering I am interested in the range of the ratio between V1 and

V2,

should I be looking at doing a different analysis?

I am so dumb, any help is appreciated,

Dan.