CODEWITHSUNDEEP
pythonmatrixrandomelement
DrakonianD
DrakonianD

Reputation: 39

How to select a random position from a 3x3 matrix

I have this mathematical problem where I need to select a random element from a matrix. Now I have the code for the matrix and other bits. but I tried to select a random element by using below code but It always selects one complete row, instead of a random single element.

def randSelect(self):
    return self.matrix[random.randrange(len(self.matrix))]

Here is the complete code as well

class Matrix():
    def __init__(self, cols, rows):
        self.cols = cols
        self.rows = rows

        self.matrix = []
        for i in range(rows):
            selec_row = []
            for j in range(cols):
                selec_row.append(0)
            self.matrix.append(selec_row)
    def setitem(self, col, row, v): 
        self.matrix[col-1][row-1] = v

    def randSelect(self):
        return self.matrix[random.randrange(len(self.matrix))] 

    def __repr__(self):
        outStr = ""
        for i in range(self.rows):
            outStr += 'Row %s = %s\n' % (i+1, self.matrix[i])
        return outStr

    a = Matrix(3,3)
    a.setitem(1,2,10)
    a.setitem(1,3,15)
    a.setitem(2,1,10)

Upvotes: 0

Views: 1106

Answers (4)

Jared Mackey
Jared Mackey

Reputation: 4158

Here is my solution. I am using a namedtuple as the return so you can get the position of that value as well. 

import random
from collections import namedtuple

RandomValue = namedtuple("RandomValue", ("Value", "RowIndex", "ValueIndex"))


class Matrix():
    def __init__(self, cols, rows):
        self.cols = cols
        self.rows = rows

        self.matrix = []
        for i in range(rows):
            selec_row = []
            for j in range(cols):
                selec_row.append(0)
            self.matrix.append(selec_row)

    def setitem(self, col, row, v):
        self.matrix[col - 1][row - 1] = v

    def randSelect(self):
        row = self.matrix[random.randrange(len(self.matrix))]
        value = random.choice(row)
        return RandomValue(value, self.matrix.index(row), row.index(value))

    def __repr__(self):
        outStr = ""
        for i in range(self.rows):
            outStr += 'Row %s = %s\n' % (i + 1, self.matrix[i])
        return outStr


a = Matrix(3, 3)
a.setitem(1, 2, 10)
a.setitem(1, 3, 15)
a.setitem(2, 1, 10)
print(random_val.RowIndex)
print(random_val.ValueIndex)
print(random_val.Value)

Upvotes: 1

furas
furas

Reputation: 142631

def randSelect(self):
    row = random.randrange(self.rows)
    col = random.randrange(self.cols)
    return self.matrix[row][col]

Upvotes: 3

0xtvarun
0xtvarun

Reputation: 698

you can have a function generate random numbers in the range of your indices and you can use those indices to call a random location in your array

    from random import randint
    i = (randint(0,9)) #assuming your range for i is from 0-9
    j = (randint(0,9)) #assuming your range for j is from 0-9

Upvotes: 0

Scott M.
Scott M.

Reputation: 7347

Your randselect function needs to access self.matrix with two indices. It's an array of arrays, so with only one set of square brackets you get back an array. You'll need a second access to get an individual element.

def randSelect(self):
    row = self.matrix[random.randrange(len(self.matrix))]
    return row[random.randrange(len(row))]

Upvotes: 0

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