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Question

I have a pandas Panel that is long, wide, and shallow. In reality it's bigger but for ease of example, let's say it's 2x5x6:

panel=pd.Panel(pd.np.random.rand(2,3,6))

I have a Series that is the length of the shortest dimension - in this case 2:

series=pd.Series([0,1])

I want to multiply the panel by the series, by broadcasting the series across the two other axes.

1. Using panel.mul doesn't work, because that can only take Panel s or DataFrame s, I think

   panel.mul(series) # returns None

2. Using panel.apply(lambda x: x.mul(series), axis=0) works, but seems to do the calculation across every combination of series, in this case 3x6=18, but in reality >1m series, and so is extremely slow.

3. Using pd.np.multiply seems to require a very awkward construction:

   pd.np.multiply(panel, pd.np.asarray(series)[:, pd.np.newaxis, pd.np.newaxis])

Is there an easier way?

Answer 1

I don't think there's anything wrong conceptually with your last way of doing it (and I can't think of an easier way). A more idiomatic way to write it would be

import numpy as np
panel.values * (series.values[:,np.newaxis,np.newaxis])

using values to return the underlying numpy arrays of the pandas objects.