ENH/VIS: Dataframe bar plot can now handle align keyword properly

[sinhrks]

Closes #4525.

I modified the BarPlot internal alignment to meet line coordinates. Previously, BarPlot doesn't pass align keyword to matplotlib (thus matplotlib uses align='edge'), but it adjusts bar locations to looks like align='center'.

Now BarPlot pass align=center to matplotlib by default and ticks are being locates on integer value starts from 0 (0.0, 1.0 ...). Drawing bar and line on the same axes looks like below.

Output using current master:

Output after fix

[TomAugspurger]

Did you mean to remove this instead of replacing with

axes = self._check_bar_alignment(df, kind='bar', width=.9, stacked=False)

?

EDIT: Nevermind, it's further down. Github tricked me.

[TomAugspurger]

Thanks for this.

We may want a little warning in the release notes that this will change the look of the default output. I'm onto sure how guarantee plots being identical from one version to another.

You have a few magic numbers in the _check_bar_alignment function, like in tickoffset = width * (position - 0.5) + p.get_width() * 1.5. Are the .5 and 1.5 just constants that matplotlib uses?

I had a couple of notes inline, but overall this looks good. If you look at those and rebase I'll get it merged. Thanks.

[sinhrks]

Thanks for your confirmation. I added decorators / warning description in what's new txt, and rebased.

Fixed numbers in _check_bar_alignment is derived from BarPlot class logic (line 1690 of plotting.py).

• width * (position - 0.5) derived from position 's default (0.5). Because BarPlot now specifies the center-bottom coordinate of bar, no adjustment should be done when position is 0.5. Thus, it should be substituted.
• p.get_width() * 1.5 is derived from previous version's logic. BarPlot has draw non-stacked plot starting from (i +1) * width location (line 1766 of plotting.py). Now we have to specify the bar location, it should be changed to (i + 1.5) * width. Thus, to get the same offset as the previous logic, I used 1.5 to get the offset.

[jreback]

this should not be here, instead in the plotting.rst (if where you show how to work with this option, if necessary)

[sinhrks]

OK. I have understood to write a warning about backward-compatibility in release note, but it should be in plotting.rst, or simply removed? I think usage is not necessary because the align keyword works as the same as matplotlib.

I'll correct my typo once confirmed where the description should be (or removed).

[jreback]

ok so move both the release note and the v0.14.0 note to the API section - change from an actual warning block to just text in the note (no need for a separate warning block)

[sinhrks]

Sure. Descriptions are under API Changes section, and corrected typo and warning block.

[jreback]

ok by me... @TomAugspurger if ok, then go ahead and merge

[TomAugspurger]

Looks good. Thanks