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Pandas DataFrame | dot method

Pandas
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Documentation
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DataFrame
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Binary Operators
schedule Jul 1, 2022
Last updated
local_offer PythonPandas
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Pandas DataFrame.dot(~) method is used to compute matrix-vector and matrix-matrix multiplication.

Parameters

1. arr | array-like or Series or DataFrame

The vector or matrix with which to compute the product.

Return Value

A Series is returned if the return value has only one column, otherwise a DataFrame is returned.

Examples

Consider the following DataFrame:

df = pd.DataFrame({"A":[1,2], "B":[3,4]})
df
A B
0 1 3
1 2 4

Performing a matrix-vector multiplication

To perform a matrix-vector multiplication:

df.dot([5,6])
0 23
1 34
dtype: int64

Here, we are performing the following calculation:

$$\begin{pmatrix}  1&3\\  2&4 \end{pmatrix} \begin{pmatrix}  5\\  6 \end{pmatrix}= \begin{pmatrix}  23\\  34 \end{pmatrix}$$

The return type is a Series since the result only has one column.

Performing a matrix-matrix multiplication

To perform a matrix-matrix multiplication:

df.dot([[5,6], [7,8]])
0 1
0 26 30
1 38 44

Here, we are performing the following calculation:

$$\begin{pmatrix}  1&3\\  2&4 \end{pmatrix} \begin{pmatrix}  5&6\\  7&8 \end{pmatrix}= \begin{pmatrix}  26&30\\  38&44 \end{pmatrix}$$

Since the return value has multiple columns, we get a DataFrame instead of a Series.

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Published by Isshin Inada
Edited by 0 others
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