Addressing transform sort order with null values

[oshikryu]

Updating sort function to handle null value case
Changing sort transform tests to include null value

This should fix the issue in #4784

Example working codepen:
https://codepen.io/oshikryu/pen/rNOjeZb

[alexcjohnson]

Thanks for the PR @oshikryu - looking good, and your test additions are excellent!

I think we want to treat any sort of invalid data the same as null - which, after running through d2c, becomes BADNUM from src/constants/numerical. BADNUM is just undefined but for clarity and consistency we prefer to use the named constant.

So this would look something like:

var ac = d2c(a.v);
var bc = d2c(b.v);
if(ac === BADNUM) {
    return -1;
}
if(bc === BADNUM) {
    return 1;
}
return ac - bc;

Also I suppose this can be up for discussion, but in several other contexts (eg Dash DataTable) we sort null values always at the end - the idea being you want them out of the way where you mostly ignore them. Here you're sorting them as "extra negative", which puts them last when sorting descending, but FIRST when sorting ascending.

[oshikryu]

Good point about "extra negative" for BADNUM values. I added the reference to BADNUM in the sort and updated the tests

[oshikryu]

I'm not really sure what downstream errors were produced with this change. I could use some guidance @alexcjohnson

[alexcjohnson]

Excellent, thanks for the change, this looks good to me! 💃 @archmoj please merge when you're ready.

I'm not really sure what downstream errors were produced with this change.

Were the tests failing before your force push? Don't worry about it, the tests have been a little bit flaky lately and sometimes need to be rerun. For future reference though we discourage force pushes in this repo once a PR is open, as it can confuse the review process.