perspective-viewer-d3fc: Double group-by in Y-Bar not grouping bars correctly

[mhkeller]

Bug Report

Steps to Reproduce:

1. Load this dummy data of student exams in different subjects and periods: https://gist.github.com/mhkeller/8831f579f814af2a7415e043457d4e56
2. Select the Y-bar visualization
3. Group by period and exam_subject

Expected Result:

I would expect the bars within each period group to not have any white space between them.

Here's an example from the d3fc website that I expect it to look similar to.

Actual Result:

The bars are evenly spaced, making the chart harder to read since each of the groups is not visually separate.

Environment:

"@finos/perspective": "^2.7.0",
"@finos/perspective-viewer": "^2.7.0",
"@finos/perspective-viewer-d3fc": "^2.7.0",
"@finos/perspective-viewer-datagrid": "^2.7.0",

Chrome 119 and Firefox 120

[mhkeller]

@timkpaine If you have any suggestions on what might be causing this bug, I can try to take a look.