Converting pandas DatetimeIndex to 'float days format' with Matplotlib.dates.datestr2num

Question

Some Matplotlib methods need days in \'float days format\'. datestr2num is a converter function for this, but it falls over with the relevant pandas objects:

Answer 1

You can use the to_pydatetime method of the DatetimeIndex (this will convert it to an array of datetime.datetime's, and mpl.dates.date2num will know how to handle those):

mpl.dates.date2num(df.index.to_pydatetime())

The reason that date2num does not natively handle a pandas DatetimeIndex, is because matplotlib does not yet support the numpy datetime64 dtype (which is how the data are stored in a DatetimeIndex).