Matrix multiplication using pandas DataFrames

Overview:

The dot() method of pandas DataFrame class does a matrix multiplication between a DataFrame and another DataFrame, a pandas Series or a Python sequence and returns the resultant matrix.
When two matrices one with columns 'i' and rows 'j' and another with columns 'j' and rows 'k' are multiplied - 'j' elements of the rows of matrix one are multiplied with the 'j' elements of the columns of the matrix two and added to create a value in the resultant matrix with dimension (ixk).

Example - Multiplying two matrices of same dimensions:

import pandas as pd

# Data

matrix1 = [(1, 1, 2),

(0, 2, 1),

(2, 0, 1)];

matrix2 = [(2, 0, 2),

(1, 1, 1),

(2, 2, 2)];

# Data loaded into pandas DataFrames

dataFrame1 = pd.DataFrame(data=matrix1);

dataFrame2 = pd.DataFrame(data=matrix2);

print("Matrix1:");

print(dataFrame1);

print("Dimension:");

print(dataFrame1.shape);

print("Matrix2:");

print(dataFrame2);

print("Dimension:");

print(dataFrame2.shape);

# Multiply the matrices: Matrix1 and Matrix2

result = dataFrame1.dot(dataFrame2);

# Print the result of matrix multiplication

print("Matrix multiplication – resultant matrix:");

print(result);

print("Dimension of the resultant matrix:");

print(result.shape);

Output:

Python example program for multiplying two matrices where matrices are pandas dataframes

Example: Multiplying matrices of different dimensions

import pandas as pd

data1 = [(0,1,2),

(3,4,5),

(6,7,8)];

matrix_3x1 = (1, 2, 3);

matrix_3x3 = pd.DataFrame(data=data1);

# Note that in this example dot is invoked with a plain python tuple.

# Not with a pandas DataFrame...not with a pandas series

resultant = matrix_3x3.dot(matrix_3x1);

print("Matrix1:DataFrame")

print(matrix_3x3);

print("Shape of matrix1:")

print(matrix_3x3.shape);

print("Matrix2:Tuple")

print(matrix_3x1);

print("Shape of matrix2:")

print("(%d,%d)"%(len(matrix_3x1), 1));

print("Two matrices multiplied. Resultant matrix is:")

print(resultant);

print("Type of resultant matrix is:")

print(type(resultant));

print("Shape of resultant matrix:")

print(resultant.shape);

Output:

Matrix multiplication using a pandas dataframe and a python tuple