import math
import csv

def load_csv(filename):
    lines = csv.reader(open(filename,"r"))
    dataset = list(lines)
    headers = dataset.pop(0)
    return dataset,headers

class Node:
    def __init__(self, attribute):
        self.attribute = attribute
        self.children = []
        self.answer = ""

def subtables(data, col, delete):
    dic = {}
    coldata = [row[col] for row in data]
    attr = list(set(coldata))
    for k in attr:
        dic[k] = []
    for y in range(len(data)):
        key = data[y][col]
        if delete:
            del data[y][col]
        dic[key].append(data[y])
    return attr,dic

def entropy(S):
    attr = list(set(S))
    if len(attr) == 1:
        return 0
    counts = [0,0]
    for i in range(2):
        counts[i] = sum([1 for x in S if attr[i]==x])/(len(S)*1.0)
    sums = 0
    for cnt in counts:
        sums += -1*cnt*math.log(cnt,2)
    return sums