functional interface for deleting columns

[tpapp]

We have delete!, but DataFrame is particularly nice for a functional style when subsetting/transforming columns, so it would make sense to have something like

dropcols(df::AbstractDataFrame, cols) = df[setdiff(names(df), cols)]

[nalimilan]

I guess we could support this via negated indexing instead of adding a new function?

[tbeason]

I define this function at the top of literally any script where I am using DataFrames (although I'll probably switch to your version because it is was more compact).

dropcol(d,args...) = @select(d, filter(x -> !(x in args),names(d)))

[bkamins]

We now support Not.