Python Matrix

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Index

1. Definition
2. Functions
   • Shape
   • Create matrix

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Definition

Bi-dimensional array organised by rows and column (list of lists)

matrix_2x1 = [ [0], [1] ] 
 
matrix_3x2 = [ [0,1], [1,2], [3,4] ] 

Example:

How to access an element of the matrix in the third row and second column element = matrix[3][2] element = matrix[r][c]

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Functions

Shape

Function that calculates the number of row and columns of a matrix

def shape(mat):
    # immediatly check empty matrix
    if len(mat) == 0 or len(mat[0]) == 0:
        return 0, 0
 
    r = len(mat) # Calculare number of rows
    c = len(mat[0]) # Calculate number of columns
    return r, c

Create matrix

Function that generates an empty matrix or a matrix with the same value every where

def create_matrix_long(r,c,value=0):
    # define matrix
    matrix = []
    # for each row
    for each_r in range(r):
        # define row
        row = []
        # for each col
        for each_c in range(c):
            # append the col to the row
            row.append(value)
        # append the row to the matrix
        matrix.append(row)
    return matrix    

def create_matrix_short(r, c, value=0):
    '''
    a single for loop
    '''
    matrix = []
    for each_r in range(r):
        matrix.append([value] *c )
    return matrix

def create_matrix_lc(r, c, value=0):
    '''
    with list comprehnsion
    '''
    return [ [value] * c for each_r in range(r) ]

def create_matrix_map(r, c, value=0):
    '''
    with map and lambda function
    '''
    return list(map(lambda each_row: [value] * c, range(r)))

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