Convert all column metadata to either String or Symbol (where possible)

[ParadaCarleton]

When I load Stata files, I get an odd mix of Strings and Symbols for column metadata, which means the metadata dictionary has Any as the value type. Converting all strings to symbols should help with this.

[junyuan-chen]

@ParadaCarleton Thank you for reporting the issue! Could you produce a small Stata file (something artificial with just a couple of rows) that allows reproducing what you observed?

[ParadaCarleton]

Unfortunately I don't have something small, since I pulled the .dta file that had this problem off the internet 😅

But the file I tried to load is here. The main problem is just that the dictionaries don't convert all values into strings. (Keys can be either strings or symbols without issue.)