Output should match input

[johnmackintosh]

Currently outputs a data.table
If dataframe or tibble is input, it's reasonable to expect the same format is returned.
Needs to import from tibble though, so need to check the weight of dependencies

[johnmackintosh]

low priority - pending re-write of internals to allow for NSE

[johnmackintosh]

{collapse} has functions to quickly change between tibble/ data.frame/ data.table so reminder to investigate the logic and if necessary import those to help with this