When exporting a data.frame in CSV, one useful option is to append the contents to an existing file (eg. when processing in batches). In data.table::fwrite there is an argument append that does precisely this, of course omitting the column names when appending.

If we try this using rio::export, it doesn't work because col.names is always set to TRUE in export_delim.

rio::export(iris[1:2,], "file.csv")
rio::export(iris[1:2,], "file.csv", append = TRUE)

$ cat file.csv
Sepal.Length,Sepal.Width,Petal.Length,Petal.Width,Species
5.1,3.5,1.4,0.2,setosa
4.9,3,1.4,0.2,setosa
Sepal.Length,Sepal.Width,Petal.Length,Petal.Width,Species
5.1,3.5,1.4,0.2,setosa
4.9,3,1.4,0.2,setosa

To solve this we need to manually set col.names = FALSE, but it should use the default in fwrite that writes the column names if the file does not exist, or omits if it does.

What do you think?

Thanks!