[R] incorrect number of levels

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Chagaris, Dave
> Sent: Friday, October 08, 2010 12:04 PM
> To: r-help at r-project.org
> Subject: [R] incorrect number of levels
> 
> I have a data set 382 rows and  63 columns.  One of the 
> columns is bay, and there are 6 bays.  But, the number of 
> levels for this factor is 7 when it should be six because 
> there is some 'blank' level "".  When I subset for the blank 
> level "", I get 0 rows.  What in my data could be causing 
> this?  Thanks.

There are lots of ways to make such a dataaet.  It could be
caused by read.table(sep=",",file) where file contains two
adjacent commas and you later removed the offending row
  > d <- read.table(sep=",",
      textConnection("101,,201\n102,two,202\n103,three,203\n"))
  > d <- d[-1,]
  > levels(d$V2)
  [1] ""      "three" "two"
and you later removed the offending row.

You can get rid of the unused levels by passing it through
factor()
  > levels(factor(d$V2))
  [1] "three" "two"
and you may as well use the opportunity to give it levels
in the order you want
  > str(factor(d$V2, levels=c("two","three")))
   Factor w/ 2 levels "two","three": 1 2

  > d$V2 <- factor(d$V2, levels=c("two","three"))

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> >    dim(datmtx)
> [1] 382  63
> 
> 
> >     datmtx$bay
>   [1] TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB 
> TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB 
> TB TB TB TB TB TB TB TB TB TB TB TB
>  [51] TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB 
> TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB 
> TB TB TB TB TB TB TB TB TB TB TB TB
> [101] TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB 
> TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB TB 
> TB TB TB TB TB TB TB HI TB HI TB TB
> [151] TB TB TB TB TB HI TB HI HI HI TB HI HI HI TB HI HI HI 
> HI HI HI HI HI TB TB TB TB CH CH TB CH CH CH CH CH CH CH CH 
> CH CH TB TB CH CH CH CH CH CH CH CH
> [201] CH CH CH CH CH CH CH CH CH CH CH CH CH CH CH CH CH CH 
> CH CH TB HI HI HI TB HI HI TB TB TB TB TB TB TB TB TB TB HI 
> TB TB TB TB TB TB TB TB TB TB TB TB
> [251] TB HI HI HI CH CH CH CH CH CH CH CH CH CH HI HI CH CH 
> CH CH CH CH CH CH CH CH CH CH TB TB TB TB TB TB TB TB TB TB 
> CH CH AP AP AP AP AP AP HI HI HI CH
> [301] CH CH CH AP AP TB TB AP AP AP AP AP AP SA BB BB TB TB 
> TB TB AP HI AP SA AP HI AP AP HI HI TB HI AP SA AP AP AP AP 
> AP AP AP AP SA AP AP SA AP AP AP SA
> [351] SA SA AP AP AP CH CH CH CH CH AP BB BB BB BB BB TB CH 
> CH CH CH CH CH CH CH CH CH CH CH CH CH CH
> Levels:  AP BB CH HI SA TB
> 
> >     levels(datmtx$bay)
> [1] ""   "AP" "BB" "CH" "HI" "SA" "TB"
> 
> >     nlevels(datmtx$bay)
> [1] 7
> 
> David Chagaris
> Associate Research Scientist
> Florida Fish and Wildlife Conservation Commission
> Florida Fish and Wildlife Research Institute
> 100 8th Ave SE
> St. Petersburg, FL  33701
> (727) 896-8626 ext. 4305
> (727) 893-1374 fax
> 
> 
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