Read to dataframe

[pdb5627]

I created a new function that reads all the PL4 simulation data into a dataframe. For my use, this is easier than the getVarData function that already existed in the library.

In a comment, I added a reference to the PlotXY open-source code where it provides some information about how the PISA PL4 file is structured.

[ldemattos]

Dear @pdb5627,

First of all many thanks for your very interesting contribution. I totally understand that the usage of a full pandas dataframe may make more sense for someone. When I wrote the readPL4 my use case was the reading of multilples large PL4 files, in doing so, the memory usage was a concern.

I worked a little bit on your code trying to make it fit on what was already done in readPL4. First of all, I moved all your modifications for the new _py3 code with your prior contributions. And then, I started to actually doing an harmonization effort. I still have to backport the new features to python 2 code base.

Please, take a look at the branch pdb5627-read_to_dataframe . Check if my modifications don't spoil your usage and/or you have more comments. The more meaningful modification that I did was the way the column name in dataframe was build. As far I know, spaces matter in atp node naming, and cutting them out my be problematic, e.g. var 'A A' will be equal to 'AA'.

Thanks as well for the variable conversion codes found in PlotXY repository code. Very useful piece of information.

Again, thanks very much for your contributions.

Best regards,
LMNM

EDIT: Sorry for taking so long to review this P-R.

[ldemattos]

The python2 interpreter is able to run the python3 version without problems. In doing, no need to keep two different versions. Thus I stepped back in having two different versions, and keeping a single version based on python3 will be the way to go.