Reduce the number of for loops from json_parser

[PietrH]

The JSON parser is difficult to read, it would be good to reduce the number of for loops. I'm going to produce a start for Lynn to have a look at, and see if she wants to further implement it.

The for loops are not currently a breaking issue, so this is low priority.

This is also a demo for Lynn to see how branching and conflict resolution works in GIT.

[PietrH]

@LynnDelgat I've put some draft code in https://github.com/LynnDelgat/MIDS-Lynn/blob/pieter-json-parser/src/parse_json_schema_purrr.R

You can adapt it to split conditions as in the current proposal, hopefully it's enough to get you going with purrr and avoiding the if trees in for loops to filter out lists.

Alternatively you might want to write it out using list comprehension: https://cran.r-project.org/web/packages/comprehenr/vignettes/Introduction.html

I would probably fall back on rlang eg. : https://thomasmailund.medium.com/list-comprehension-in-r-3579b6e1dab9, but I find purrr more readable than list comprehensions and I'm not really fluent in them to be honest.