Hello,


I am a new user to R and have a(proabably very basic)  question relating to
a boxplot with eleven sites in a river system where i measured Chlorophyll a
concentrations.

The eleven sites are made up of three sites above a point source pollution
site; three sites below this pollution source and five sites in a different
unaffected river.

The following code is for a simple plot of the data


boxplot(Chl~Site,data=p,col="slategrey",
boxwex=0.75,xlab="Site",ylim=c(0,250))
mtext(expression("Chlorophyll a" (mg/m^2)),side=2,line=2.75,cex=0.7)


The question is:

1) In my data sheet I have the sites grouped together (i.e. above pollution,
below and  unaffected), but the default setting in R seems to place these
alphabetically on the x-axis rather than in the order I have entered into
the spreadsheet. How to i correct this?

Many thanks,

Phil

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