CODEWITHSUNDEEP
pythonpandasnumpymatrix
apotamkinn
apotamkinn

Reputation: 61

How to subtract matrices in Python properly?

I've been trying to subtract two matrices (not sure if they are really matrices since one of them is pandas series) but the result is not true. I added the code and outputs, how can I get the correct 200X1 shape result?

*X is 200x4 and w is 4x1

Code

Upvotes: 1

Views: 530

Answers (2)

sagi
sagi

Reputation: 40481

You can reshape y_hat :

y - y_hat.reshape(-1,1)

The reason you get (200,200) is because of numpy broadcasting, it treats y_hat as (1,200), so in order for the shapes to match, numpy broadcasts y into (200,200) and y_hat into (200,200) and then does the substraction.

Upvotes: 1

Corralien
Corralien

Reputation: 120439

Maybe it could help:

rng = np.random.default_rng(2022)
df = pd.DataFrame(rng.integers(0, 10, (5, 4)))
sr = pd.Series(rng.integers(0, 10, (5, )))

>>> df
   0  1  2  3
0  7  2  7  0
1  1  6  9  0
2  0  6  8  7
3  8  1  5  0
4  0  4  8  9

>>> sr
0    3
1    9
2    0
3    2
4    6
dtype: int64

>>> df - sr  # does not work
   0  1  2  3   4
0  4 -7  7 -2 NaN
1 -2 -3  9 -2 NaN
2 -3 -3  8  5 NaN
3  5 -8  5 -2 NaN
4 -3 -5  8  7 NaN

>>> df.sub(sr, axis=0)  # work
   0  1  2  3
0  4 -1  4 -3
1 -8 -3  0 -9
2  0  6  8  7
3  6 -1  3 -2
4 -6 -2  2  3

Upvotes: 1

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