[R] Problem with subsets and xyplot

[Peter Flom]

Hello

I have a dataframe that looks like this

     MSA                          CITY HIVEST YEAR   YR CAT
1   0200  Albuquerque                     0.50 1996 1996   5
2   0520  Atlanta                        13.00 1997 1997   5
3   0720  Baltimore                      29.10 1994 1994   1
4   0720  Baltimore                      13.00 1995 1995   5
5   0720  Baltimore                       3.68 1996 1996   3
6   0720  Baltimore                       9.00 1997 1997   5
7   0720  Baltimore                      11.00 1998 1998   5
8   0875  Bergen-Passaic                 51.80 1990 1990   5


many more rows....

I would like to create some xyplots, but separately for MSAs that are
high, moderate or low on HIVEST.  Here's what I tried

#### READ IN DATA AND RECODE SOME VARIABLES
attach(hivest)

cat <- CAT
cat[cat > 5] <- 6


msa <- as.numeric(MSA)
msa[msa == 7361] <- 7360
msa[msa == 7362] <- 7360
msa[msa == 7363] <- 7360

msa[msa == 5601] <- 5600
msa[msa == 5602] <- 5600

msa[msa == 6484] <- 6483


####   FIND MEANS FOR EACH MSA, FOR SUBSETTING LATER
meanbymsa <- aggregate(HIVEST, by = list(msa), FUN = mean, na.rm = T)

#### meanbymsa[,2] gives me the column I want; the 25%tile of this
column is about 3.1.

but when I try

plot1 <- xyplot(HIVEST~YEAR|as.factor(msa),  pch = LETTERS[cat], subset
= (meanbymsa[,2] < 3.1))
plot1


I don't get what I expect.  No errors, and it is a subset, but the
subset is NOT MSAs with low values of HIVEST.


Any help appreciated.


Peter




Peter L. Flom, PhD
Assistant Director, Statistics and Data Analysis Core
Center for Drug Use and HIV Research
National Development and Research Institutes
71 W. 23rd St
http://cduhr.ndri.org
www.peterflom.com
New York, NY 10010
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