Keep original features order
The arrow writer was supposing that the columns were always in the sorted order. I just pushed a fix to reorder the arrays accordingly to the schema. It was failing for many datasets like squad and obviously it broke everything Feel free to revert my commit. I can investigate this in the coming days @lhoestq I do not understand when you say:
> It was failing for many datasets like squad

All the tests were green after my last commit. > All the tests were green after my last commit.

Yes but loading the actual squad dataset was failing :/

When loading a Dataset from a JSON file whose column names are not sorted alphabetically, we should get the same column name order, whether we pass features (in the same order as in the file) or not.

I found this issue while working on #2366.