bug: when a variable only has one value nothing is drawn

[heike]

data(flea, package="GGally")
flea$one <- 1
flea %>%
ggplot(aes(vars = vars(1:8))) +
geom_pcp(aes(colour=species))

[yaweige]

There is also a "removed data" case in the README for "wide" data set which might be related

[yaweige]

I believe this is caused by transform_pcp(), where (max()-min()) is used as denominator

[yaweige]

We should also coerce the character variables to factor variables in the gather_pcp(), otherwise, it won't work with charactor variables.

[yaweige]

And also take care of the classes of variables, for example, when it is an "integer", after transformation, it should be "numeric", but it is still recorded as "integer" which is carried over from gather_pcp. This could also happen in coercing character vectors. When the class is "charactor", the Statpcp will produce an error.

[yaweige]

But "integer" is fine