[R] Plot grouped histograms

Peter Dalgaard p.dalgaard at biostat.ku.dk
Thu Oct 9 22:10:02 CEST 2008

soeren.vogel at eawag.ch wrote:
> r11 -- r16 are variables showing a reason for usage of a product in 6 
> different situations. Each variable is a factor with 4 levels imported 
> from a SPSS sav file with labels ranging from "not important" to "very 
> important", and NA's for a sample of N = 276.
> (1) I need a chi square test of independence showing that the reason 
> does not differ depending on the situation.
> (2) I need a single coloured histogram plot. The x axis should be 
> grouped by the 6 situation with small space between the groups, each 
> group should show different bars for each factor value ("not 
> important", "little...", ..., "NA's"), but NA's is not necessary.
> I've been googling the whole day, searching the mailing list and 
> handbooks, and struggled through the somewhat R programmer specific 
> documentation. Beeing a newby in R, I'm now afraid that I have to go 
> back to SPSS and Excel where my tasks would be a work of an hour. But 
> I was told "euphoric" that R may solve many of the problems I have 
> (and don't like) with SPSS, or having to separate calculation

dd <- subset(yourdata, select=r11:r16)

(1) is not a straightforward chi-square.... What _would_ you do in SPSS? 
You might do it in an hour, but I suspect it wouldn't be right.... In R, 
possibly, friedman.test(as.matrix(dd))

M <- sapply(dd,table)
barplot(M, beside=TRUE)

(getting the axis labels exactly right can be a bit tricky, though.)

> (SPSS, Excel by hand) and plotting (GNUplot).
> So my two questions are: How can I easily solve my 2 tasks? Secondly, 
> is R really recommended for R newbys in daily work?
> Thank you for any help
> Sören
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   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark      Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)              FAX: (+45) 35327907

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