barplot() x axes are not updated after removal of categories from the dataframe

Hi all,
I'd be grateful for your help. I am a new user struggling with a barplot
issue.

I am plotting categories (X axis) and their mean count (Y axies) with
barplot().

The first call to barplot works fine.

I remove records from the dataframe using final=[!final$varname == "some
value",]

I echo the dataframe and the records are no longer in the dataframe.

When I call plot again however, the X axis still contains the removed
category values albeit with a count of 0.

How can I stop the removed categories appearing in the barplot? Are they
stored globally after the first barplot call?

thanks in advance for your help.

R

When you subset a factor, the unused levels are not removed by default.
This is intentional to preserve these characteristics for subsequent
operations such as modeling.

You are presumably using something like:

  table(final$varname)

to create the counts used in barplot().

As an example, using the iris dataset:

table(iris$Species)

setosa versicolor  virginica
        50         50         50


iris2 <- subset(iris, Species != "setosa")

table(iris2$Species)

setosa versicolor  virginica
         0         50         50

Note that even though I removed records from iris where Species ==
"setosa", it still shows in the table.

You would need to do the following:

iris2$Species <- factor(iris2$Species)

table(iris2$Species)

versicolor  virginica
        50         50

Using factor() on the column removes the unused levels.

See  ?"[.factor" for more information.

HTH,

Marc Schwartz