R help - Oct 2010 - 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.
>    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


	[[alternative HTML version deleted]]

On Oct 8, 2010, at 3:04 PM, Chagaris, Dave wrote:
> 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.
How did you do the subset?
> What in my data could be causing this?  Thanks.
>
>>   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"
What do you get with:

which(!datmtx$bay %in% c( "AP", "BB", "CH",
"HI," "SA", "TB") )

-- 
David.
>
>>    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
>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT

> -----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
> 
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>