> I therefore wish to examine all values of urban.long[,3] which are
> greater than 1. I have tried the following, but receive error
> messages each time:
> > hist(urban.long[,3]>1)
> Error in hist.default(urban.long[, 3]> 1) : 'x' must be numeric
> > hist(urban.long[urban.long[,3]>1])
> Error in `[.data.frame`(urban.long, urban.long[, 3]> 1) :
> undefined columns selected
> > hist(urban.long[urban.long[,3]>1])
> Error in `[.data.frame`(urban.long, urban.long[, 3]> 1) :
> undefined columns selected
> > hist(as.numeric(urban.long[urban.long[,3]>1]))
> Error in `[.data.frame`(urban.long, urban.long[, 3]> 1) :
> undefined columns selected
> > hist(as.numeric(as.character(urban.long[urban.long[,3]>1])))
> Error in `[.data.frame`(urban.long, urban.long[, 3]> 1) :
> undefined columns selected
Again the probelm is the indeing being wrong. What you wand can be
achieved by this:
hist( urban.long[urban.long[,3]>1, 3] )
So your second approach was almost right but again did not return
column 3 as a vector.
You may also want to have a look at the manual page for the subset()
function which sometimes (or to some people) feels easier than logical
subsetting.
cu
Philipp
--
Dr. Philipp Pagel
Lehrstuhl für Genomorientierte Bioinformatik
Technische Universität München
Wissenschaftszentrum Weihenstephan
85350 Freising, Germany
http://mips.gsf.de/staff/pagel
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