generate_data.py

"""
  generate_data.py      :   This file contains the Knapsack class for creating random weight-value vectors and
                            writing it to json files.
  File created by       :   Shashank Goyal
  Last commit done by   :   Shashank Goyal
  Last commit date      :   30th October 2020
"""

# json module used to store and load the knapsack objects in json files
import json
# choice method to select an objects from a list of objects
from random import choice

# numpy module for dot product, cumulative sum, random integer generation
import numpy as np


class Knapsack:
    """Class to represent and store Knapsack Problem Object.

    Attributes: 
        n       (int)                   : number of items in the knapsack.
        weights (np.ndarray or list)    : contains the weights vector.
        values  (np.ndarray or list)    : contains the  corresponding value vector.
        capacity (int)                  : capacity value of the knapsack.

    """

    def __init__(self, n: int, upper_seed: int = 51, json_fname: str = None):
        """Initialization for Class.

        Args:
            n           : number of items in the knapsack.
            upper_seed  : used as the upper limit on the range while generating the values.
            json_fname  : name of the file to load the knapsack object from.

        """

        # if file name is specified
        if json_fname is not None:
            # open the json file
            with open(json_fname, 'r') as json_file:
                # update the self attributes with the contents of the file
                self.__dict__ = json.load(json_file)
            # end function
            return

        # number of items
        self.n = n
        # take cumulative sum of an array of random integers to make it strictly increasing
        self.values = np.cumsum(np.random.randint(low=1, high=upper_seed, size=n))
        # take cumulative sum of an array proportional to the value vector and round off as integers
        self.weights = (np.cumsum(np.multiply(self.values, np.random.rand(n, )))).astype(np.int)
        # add weights vector to the values vector inorder to make value vector greater than weights vector
        self.values += self.weights
        # capacity is chosen as three times the weight of one of top 10 percent of the weight vectors
        self.capacity = int(3 * choice(self.weights[int(-0.1 * n):]))

        # convert values vector to list
        self.values = self.values.tolist()
        # convert weights vector to list
        self.weights = self.weights.tolist()

    def __repr__(self):
        """Implementation of `repr` dunder method.

        Returns:
            str: String representation of the class attributes.
        """
        string = "Capacity: {}\nNumber of Items: {}\nWeights: {}\nValues: {}\n".format(self.capacity,
                                                                                       self.n,
                                                                                       self.weights,
                                                                                       self.values)
        return string

    def to_numpy(self):
        """Converts the weights and values vector back to numpy arrays.
        """
        self.weights = np.array(self.weights, dtype=np.int)
        self.values = np.array(self.values, dtype=np.int)


if __name__ == "__main__":
    # number of items
    no_of_items = 10
    # upper seed
    seed = 51
    # path to save the file
    fname = './values/' + str(no_of_items) + '_values.json'

    # knapsack object
    k = Knapsack(no_of_items, seed)
    # display the contents of the knapsack object
    print(k)

    # create the file
    with open(fname, 'w') as file:
        # store the contents of the object in the file
        json.dump(k.__dict__, file)

    # ========================== Sanity Check ========================== 
    # load a new object with the contents of the file just created
    k_load = Knapsack(no_of_items, json_fname=fname)
    # display the contents of this loaded knapsack object
    print(k_load)
    print("Sanity Check Complete")