Add cycle number and charge/discharge tags in solution data

Summary Automatically provide information on cycle number and whether the data describe charge / discharge

Motivation After running an experiment, some data post-processing is needed to append information on cycle number and charge/discharge, which can be useful for further data analysis. These features could be automatically extracted and included in sol.data

Additional context Using Pandas and Numpy, I have added a couple of lines to add these features after importing the data into a DataFrame, although I do realize they may not fully describe all existing use cases for more complex charge/discharge cycles:

df["Charge/Discharge"] = np.where(df["Current [A]"] >=0, "D", "C") df["Cycle number"] = np.ceil(df["Charge/Discharge"].ne(df["Charge/Discharge"].shift()).cumsum() / 2).astype("int32")

[tinosulzer]

The way solution.data is constructed is not super straightforward, it has to evaluate pybamm symbols (variables). We could add a variable which is the sign of the current. Adding a variable for cycle number is harder

[tinosulzer]

Are you aware of solution.cycles and (e.g.) solution.cycles[0].steps, which give an easy way of splitting cycles and steps?