data_loader.R prohibitively slow

[swpease]

I tried using data_loader.R on temperature_rain_dataset_with_missing_values.tsf, and it was not working. I halted it after over an hour.

I modified the script and it now loads in a minute or so. The speedup all comes from pre-allocating lists to read the lines into. Do you want to incorporate these changes somehow -- either a pull request, modifying it on your own, etc.?

[m-muecke]

I've faced the same issue. I've written a performant version here: https://github.com/mlr-org/mlr3forecast/blob/main/R/tsf.R#L13