Incorrect processing of plot_args when using data argument

[timhoffm]

Bug report

As opposed to dicts, pandas.DataFramse etc. name in container does not check if a field exists in a numpy array. Hence, mustn't do args[1] in data unconditionally on the data type. This was spotted due to the indirectly related warning:

lib/matplotlib/tests/test_axes.py::test_structured_data
  /home/travis/build/matplotlib/matplotlib/lib/matplotlib/axes/_axes.py:52: FutureWarning: elementwise == comparison failed and returning scalar instead; this will raise an error or perform elementwise comparison in the future.
    if (not args[1] in data and

Possible fixes:

• Cleanup _plot_args_replacer logic #10872, which gets the logic straight
• or alternatively Simplify (quite a bit...) _preprocess_data #10928, which is a larger cleanup and removes _plot_args_replacer() altogether.

[tacaswell]

I have a memory of a PR special casing structured arrays recently....

[jklymak]

@timhoffm is this closed by #10872?

[timhoffm]

Yes, fixed by #10872.