New posts in levels

How can I drop unused levels from a data frame?

Why is the terminology of labels and levels in factors so weird?

r levels factors

Re-ordering factor levels in data frame [duplicate]

r dataframe levels r-faq

Reorder levels of a factor without changing order of values

r sorting levels r-faq

ggplot2 keep unused levels barplot

r ggplot2 legend levels

`levels<-`( What sorcery is this?