From: Robert Walters <pungo9nc_at_embarqmail.com>

Date: Fri, 22 Feb 2008 20:01:34 -0500

R-help_at_r-project.org mailing list

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 Sat 23 Feb 2008 - 01:05:24 GMT

Date: Fri, 22 Feb 2008 20:01:34 -0500

R folks,

As an R novice, I struggle with the mystery of subsetting. Textbook and
online examples of this seem quite straightforward yet I cannot get my
mind around it. For practice, I'm using the code in MASS Ch. 6,
"whiteside data" to analyze a different data set with similar variables
and structure.

Here is my data frame:

###subset one of three cases for the variable 'position'

* >data.b<-data.a[data.a$position=="inrow",]
** > print(data.b)
*

position porosity x y 1 inrow macro 1.40 16.5 2 inrow macro . . . . . . . . . . 7 inrow micro 8 inrow micro

Now I want to do separate lm's for each case of porosity, macro and micro. The code as given in MASS, p.141, slightly modified would be:

fit1 <- lm(y ~ x, data=data.b, subset = porosity == "macro") fit2 <- update(fit1, subset = porosity == "micro")

###simplest code with subscripting

fit1 <- lm(y ~ x, data.b[porosity=="macro"])

###following example in ?subset

fit1 <- lm(y ~ x, data.b, subset(data.b, porosity, select=macro))

None of th above, plus many permutations thereof, works. Can anyone educate me?

R-help_at_r-project.org mailing list

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 Sat 23 Feb 2008 - 01:05:24 GMT

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