[R] Beginner question: select cases

[ONKELINX, Thierry]

Your problem would be a lot easier if you coded the location in one
variable instead of three variables. Then you could calculate the means
with one line of code:

by(results$q1, results$location, mean)

With your dataset you could use
by(results$London, results$location, mean)
by(results$Rome, results$location, mean)
by(results$Vienna, results$location, mean)

see ?by for more information

And take a good look at your code. You take a subset from results and
the assign it to results. This means that you replace the original
results dataframe with a subset of it. As you take the subset for the
next city, you won't take a subset from the original dataset but for the
previous subset!

Cheers,

Thierry
------------------------------------------------------------------------
----

ir. Thierry Onkelinx

Instituut voor natuur- en bosonderzoek / Reseach Institute for Nature
and Forest

Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance

Gaverstraat 4

9500 Geraardsbergen

Belgium

tel. + 32 54/436 185

Thierry.Onkelinx op inbo.be

www.inbo.be 


-----Oorspronkelijk bericht-----
Van: r-help-bounces op stat.math.ethz.ch
[mailto:r-help-bounces op stat.math.ethz.ch] Namens Peter Wolkerstorfer -
CURE
Verzonden: maandag 25 september 2006 13:51
Aan: r-help op stat.math.ethz.ch
Onderwerp: [R] Beginner question: select cases

Hello all,

I hope i chose the right list as my question is a beginner-question.

I have a data set with 3 colums  "London", "Rome" and "Vienna" - the
location is presented through a 1 like this:
London 	Rome 	Vienna	q1
0		0	1		4
0		1	0		2	
1		0	0		3
....
....
....

I just want to calculate the means of a variable q1.

I tried following script:

# calculate the mean of all locations
results <- subset(results, subset== 1 )
mean(results$q1)
# calculate the mean of London
results <- subset(results, subset== 1 , select=c(London))
mean(results$q1)
# calculate the mean of Rome
results <- subset(results, subset== 1 , select=c(Rome))
mean(results$q1)
# calcualate the mean of Vienna
results <- subset(results, subset== 1 , select=c(Vienna))
mean(results$q1)

As all results are 1.68 and there is defenitely a difference in the
three locations I wonder whats going on.
I get confused as the Rcmdr asks me to overwrite things and there is no
"just filter" option.

Any help would be apprechiated. Thank you in advance.

Regards
Peter



___CURE - Center for Usability Research & Engineering___
 
Peter Wolkerstorfer
Usability Engineer
Hauffgasse 3-5, 1110 Wien, Austria
 
[Tel]  +43.1.743 54 51.46
[Fax]  +43.1.743 54 51.30
 
[Mail] wolkerstorfer op cure.at
[Web]  http://www.cure.at

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