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# Pandas DataFrame | dot method

schedule Aug 12, 2023
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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 B0 1 31 2 4 

## Performing a matrix-vector multiplication

To perform a matrix-vector multiplication:

 df.dot([5,6]) 0 231 34dtype: 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 10 26 301 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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