Create a pandas dataframe with differences between two vectors of unequal length

Question

I feel like I'm missing something obvious here.

I have two vectors of integers of different lengths (x and y). I'd like to create a pandas dataframe with x rows and y columns where each cell contains the difference between corresponding elements of the two vectors.

For example, given

v1 = np.array([2,4,8])
v2 = np.array([1,3])

v1 - v2

I'd like to get something back like

np.array([[ 1, -1],
          [ 3,  1],
          [ 7,  5]])

The code above is using numpy, but ultimately, I'd like to do this with Pandas.

Apologies in advance if this is a duplicate or unclear. I'm honestly not sure what terms to be searching for here.

Is your question that you want to do this fully in `pandas`? — Erfan, Nov 10 '19 at 22:29
Ideally yes, but Seb's answer below is easily converted to a pandas.DataFrame. — Daniel Keller, Nov 11 '19 at 00:04

score 2 · Accepted Answer · answered Nov 10 '19 at 22:14

2

To do this in NumPy, simply add an axis to one of the vectors:

>>> v1[:, None] - v2
array([[ 1, -1],
       [ 3,  1],
       [ 7,  5]])

Then you could convert it into a Pandas dataframe, depending on your needs. Regarding Pandas, this answer about outer products (which is the equivalent operation for multiplication instead of subtraction) may be useful to you.

answered Nov 10 '19 at 22:14

Seb

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This did the trick. Thank you! The outer product question is also helpful. – Daniel Keller Nov 11 '19 at 00:06

Create a pandas dataframe with differences between two vectors of unequal length

1 Answers1