On May 10, 2010, at 7:36 PM, John Rauser wrote:
I'm learning ggplot and am a little confused. Sometimes discrete
scales work
like I'd expect, and sometimes they don't. For example...
This works exactly like one would expect:
df<-data.frame(names=c("Bob","Mary","Joe","Bob","Bob"))
ggplot(df,aes(names))+geom_histogram()
But this yields an error:
ggplot(df,aes(names))+geom_histogram()+xlim("Bob")
Error in data.frame(count = as.numeric(tapply(weight, bins, sum,
na.rm =
TRUE))$
arguments imply differing number of rows: 0, 1
Well, a range with only one value seems a bit ... degenerate?
...as does this:
ggplot(df,aes(names))+geom_histogram()+xlim("Bob","Mary")
> str(df)
'data.frame': 5 obs. of 1 variable:
$ names: Factor w/ 3 levels "Bob","Joe","Mary": 1 3 2 1 1
... but this works fine:
ggplot(df,aes(names))+geom_histogram()+xlim("Bob","Mary","Joe")
So now that "range" covers the factor's possible values, and it
appears Hadley's coding is willing to a accept a degree of abstraction.
... and curiously, so does this:
ggplot(df,aes(names))+geom_histogram()
+xlim("Bob","Mary","Joe","Frank")
... and even more confusingly, this works perfectly:
ggplot(df,aes(names,..density..,group=1))+geom_histogram()
+xlim("Bob","Mary")
This feels like a bug, but perhaps I'm doing something dumb.
Looks dumb to me.
Can anyone
clarify?
And while I have your attention: as a ggplot novice, I often find
myself
getting cryptic error messages like the one above. Nearly always
this is
because I'm asking it to do something unreasonable, but it often
takes me
quite a long time to figure out my error. Does anyone have general
tips for
debugging ggplot commands? Anything better than summary(p)?
Use str to look at your data. gives you further information about
classes.
David Winsemius, MD
West Hartford, CT
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