thanks. but the CO2 is integer and the message says that the problem is linked to this variable and not to the character one, it is strange, isn't it?
Yeah. As before, this will be much easier with a reprex, and, since this is a new topic, I think it deserves a thread of its own.
You can include just a few rows of your data – just enough to replicate the problem (see the tidyverse.org help page.
thanks but isn't easier to write as.factor(...), so it is converted autamtically to vector, or to use stringAsFactor, so it is done for all variables?