Closes#18371

In#17289 we changed_reshape_2D (used byviolinplot andboxplot). It used to basically just callnp.asanyarray(X) which works fine with pandas. However, there is a ragged array deprecation, so#17289 now iterates over the columns using
for x in X to get each column of the matrix individually.

That is incompatible with Pandas data frame likedf = pd.DataFrame(np.random.randn(100, 3), columns=["a", "b", "c"]), which return the error in#18371, which is a regression.

Here we try to extract the matrix from X usingto_numpy() orvalues before doing the rest of the manipulations.

Note this still doesn't do the "right thing" for the column names, at least using box plot, but this fixes the regression. If the folks who use boxplot or violinplot want to do something fancier with the column names they can try to make that work in some reasonable way, but I think such fancy pandas handling really belongs in pandas, or perhaps the structured data refactor.