Source code for simplestatistics.statistics.bayesian_classifier

# I need sane division that returns a float not int
from __future__ import division

[docs]class bayesian_classifier(): """ A `naive Bayesian classifier`_. The implemention of this classifier is very closely modeled after the implementation in `simple-statistics <https://github.com/simple-statistics/simple-statistics>`_, the javascript analogue of ``simplestatistics``. You can find the javascript implementation of the Bayesian classifier `here <https://github.com/simple-statistics/simple-statistics/blob/master/src/bayesian_classifier.js>`_. .. _`naive Bayesian classifier`: https://en.wikipedia.org/wiki/Naive_Bayes_classifier Examples: Making a seventy-five/twenty-five classification. >>> model1 = bayesian_classifier() >>> model1.train({'species': 'cat'}, 'animal') >>> model1.train({'species': 'cat'}, 'animal') >>> model1.train({'species': 'cat'}, 'animal') >>> model1.train({'species': 'cat'}, 'feline') >>> model1.count 4 >>> model1.score({'species': 'cat'}) [('animal', 0.75), ('feline', 0.25)] Classifying multiple things >>> model2 = bayesian_classifier() >>> model2.train({'species': 'cat'}, 'animal') >>> model2.train({'species': 'dog'}, 'animal') >>> model2.train({'species': 'dog'}, 'animal') >>> model2.train({'species': 'cat'}, 'chair') >>> model2.score({'species': 'cat'}) [('chair', 0.25), ('animal', 0.25)] >>> model2.score({'species': 'dog'}) [('animal', 0.5), ('chair', 0)] Testing multiple properties >>> model3 = bayesian_classifier() >>> model3.train({'species': 'cat'}, 'animal') >>> model3.train({'species': 'cat'}, 'animal') >>> model3.train({'species': 'cat'}, 'animal') >>> model3.train({'species': 'cat'}, 'chair') >>> model3.train({'species': 'cat', 'color': 'white'}, 'chair') >>> model3.score({'color': 'white'}) [('chair', 0.2), ('animal', 0)] >>> mod = bayesian_classifier() >>> mod.score({'color': 'purple'}) Traceback (most recent call last): ... RuntimeError: The model has not been trained yet. Train the model before trying to score an item. """ def __init__(self): # number of items the model trained on self.count = 0 # storage for all property and category keys and values self.store = {}
[docs] def train(self, item, category): """ The method to train the instance of the Bayesian classifier on an item. Args: item: A dict of property-value pairs in the form {property_1: value1, property2: value2, . . .} for the item. category: A string of the category of the item. Returns: null """ # if the data store doesn't contain this category, # create a new key with the value being an empty # dictionary if category not in self.store: self.store[category] = {} # iterate through key/property-value pairs in item for item_key in item: item_value = item[item_key] # if it's the first time the model sees this property for this category, # add a dictionary for it if item_key not in self.store[category]: self.store[category][item_key] = {} # if this is the first time the model sees a value for this property + category, # add an entry in the dict for that property and set value to 0 if item_value not in self.store[category][item_key]: self.store[category][item_key][item_value] = 0 # increment the value tied to the property + category self.store[category][item_key][item_value] += 1 # increment count of trained items self.count += 1
[docs] def score(self, item): """ Scores a certain item based on the learning the model has done on previous items. Args: item: A dict in the form {property: value} of the item you want to score. Returns: A list containing tuples of properties and scores. The list is ordered in descending order of scores. """ if self.store == {}: raise RuntimeError('The model has not been trained yet. Train the model before trying to score an item.') # iterate through each key in the item to be scored # and then iterate through each category used in previous # .train() calls odds = {} odds_sums = {} # iterate over properties and their values in the item to score for item_key in item: # item_key is the property (e.g., color), item_value is value of property (e.g., white) item_value = item[item_key] # iterate over all categories that the model has trained on in the past for category in self.store: # if we haven't added this category to our odds dict, add it with a dict as value if category not in odds: odds[category] = {} if item_key in self.store[category]: # if the model has seen this value for this property for this category before # return the number of times divided by total training trials # we get a score for each unique property+value combination within a category if item_value in self.store[category][item_key]: odds[category][item_key + '_' + item_value] = self.store[category][item_key][item_value] / self.count # otherwise, mark it zero. else: odds[category][item_key + '_' + item_value] = 0 # MARK IT ZERO. else: odds[category][item_key + '_' + item_value] = 0 # iterate over all categories in odds dict and sum up prob values # for unique property+value combinations for category in odds: for combination in odds[category]: if combination not in odds_sums: odds_sums[category] = 0 odds_sums[category] += odds[category][combination] # return a list of properties and scores in descending order of scores return(sorted(odds_sums.items(), key = lambda x: x[1], reverse = True))