add format_list_item.data.frame

[r2evans]

Closes #6592, nested 1-column frames break print.data.table

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.60%. Comparing base (afa87e1) to head (480d8d6).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6593   +/-   ##
=======================================
  Coverage   98.60%   98.60%           
=======================================
  Files          79       79           
  Lines       14516    14517    +1     
=======================================
+ Hits        14314    14315    +1     
  Misses        202      202           

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[MichaelChirico]

Can you check if this fixes #5948, or if the fix there is related?

[MichaelChirico]

Suggested change

	test(2297.03, format_list_item(data.frame(a=1)[,0]), output = "<data.frame\\[1x0]>")
	test(2297.04, format_list_item(data.frame(a=1, b=2)[0,,drop=FALSE]), output = "<data.frame\\[0x2]>")
	test(2297.05, format_list_item(data.frame(a=1, b=2)[,0]), output = "<data.frame\\[1x0]>")
	test(2297.06, format_list_item(data.table(a=1)), output = "<data.table\\[1x1]>")
	test(2297.07, format_list_item(data.table(a=1)[0,]), output = "<data.table\\[0x1]>")
	test(2297.08, format_list_item(data.table(a=1)[,0]), output = "<data.table\\[0x0]>")
	test(2297.09, format_list_item(data.table(a=1, b=2)[0,]), output = "<data.table\\[0x2]>")
	test(2297.10, format_list_item(data.table(a=1, b=2)[,0]), output = "<data.table\\[0x0]>")
	test(2297.03, format_list_item(data.frame(a=1)[,0]), output = "<data.frame\\[1x0]>")
	test(2297.04, format_list_item(data.frame(a=1, b=2)[0,,drop=FALSE]), output = "<data.frame\\[0x2]>")
	test(2297.06, format_list_item(data.table(a=1)), output = "<data.table\\[1x1]>")
	test(2297.07, format_list_item(data.table(a=numeric())), output = "<data.table\\[0x1]>")
	test(2297.08, format_list_item(data.table(), output = "<data.table\\[0x0]>")
	test(2297.09, format_list_item(data.table(a=numeric(), b=numeric())), output = "<data.table\\[0x2]>")

[MichaelChirico]

I think the two [1x0] and [0x0] tests are redundant, right? removed in the suggested fix.

[r2evans]

I tried to do a simple expansion of 0, 1, and >1 for number of columns, and 0, 1 rows, not knowing if you were aware of other corner-cases. (This is partly because I discovered during testing that data.frame(b=1)[,0] is 1x0 whereas data.table(b=1)[,0] is 0x0. Not sure if that's intentional.) I'm happy to remove them.

[MichaelChirico]

Yes, it's intentional -- #2422 :)

[MichaelChirico]

Thanks LGTM besides the small tweak to tests & request for whether this can fix a 2nd bug.

[r2evans]

This does not affect #5948, I think my comment there covers it. LMK if there's something else for this PR.

[r2evans]

stby, I didn't QA the changes, I'll fix that fail