BUG/CLN: LinePlot uses incorrect xlim when secondary_y=True

[sinhrks]

xlim is not set properly when secondary_y=True. This is different issue from #7322.

Also, refactored secondary_y to be handled only by MPLPlot, because it will be required in future fix to pass multiple axes to df.plot, like #7069 (I'm willing to work soon..).

df = pd.DataFrame(np.random.randn(5, 5), columns=['A', 'B', 'C', 'D', 'E']) df.plot(secondary_y=True) 

df = pd.DataFrame(np.random.randn(5, 5), columns=['A', 'B', 'C', 'D', 'E']) df.plot(secondary_y=['A', 'B'], subplots=True) 

[jreback]

@cpcloud

[jreback]

@cpcloud ?

[jreback]

@sinhrks ?

[sinhrks]

@jreback Updated and rebased based on #7322 and #7515.
cc @rosnfeld

[jreback]

what did these kw's do?

[jreback]

@TomAugspurger

cc @rosnfeld ok with this?

[rosnfeld]

Not sure how deep a review I can do as I am just about to head out abroad again (more or less offline until August), but this does seem to behave properly in various ad-hoc tests, and seems to clean up a few things that surprised me when I first started looking at plotting code. A somewhat larger/more dramatic change than I would have expected, but glad to see that larger changes are possible/being done to the somewhat thorny (IMO) plotting code.

[jreback]

@sinhrks thanks! @rosnfeld thanks for the commentary

if you guys find addtl issues, pls report!