184 lines
7.6 KiB
Python
184 lines
7.6 KiB
Python
import sys
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sys.path.insert(1, '../')
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from utils.utils import *
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from collections import defaultdict
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### the ABC of data set
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class DataSet:
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"""
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A data set for a machine learning problem. It has the following fields:
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d.examples A list of examples. Each one is a list of attribute values.
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d.attrs A list of integers to index into an example, so example[attr]
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gives a value. Normally the same as range(len(d.examples[0])).
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d.attr_names Optional list of mnemonic names for corresponding attrs.
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d.target The attribute that a learning algorithm will try to predict.
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By default the final attribute.
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d.inputs The list of attrs without the target.
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d.values A list of lists: each sublist is the set of possible
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values for the corresponding attribute. If initially None,
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it is computed from the known examples by self.set_problem.
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If not None, an erroneous value raises ValueError.
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d.distance A function from a pair of examples to a non-negative number.
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Should be symmetric, etc. Defaults to mean_boolean_error
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since that can handle any field types.
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d.name Name of the data set (for output display only).
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d.source URL or other source where the data came from.
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d.exclude A list of attribute indexes to exclude from d.inputs. Elements
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of this list can either be integers (attrs) or attr_names.
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Normally, you call the constructor and you're done; then you just
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access fields like d.examples and d.target and d.inputs.
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"""
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def __init__(self, examples=None, attrs=None, attr_names=None, target=-1, inputs=None,
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values=None, distance=mean_boolean_error, name='', source='', exclude=()):
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"""
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Accepts any of DataSet's fields. Examples can also be a
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string or file from which to parse examples using parse_csv.
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Optional parameter: exclude, as documented in .set_problem().
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>>> DataSet(examples='1, 2, 3')
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<DataSet(): 1 examples, 3 attributes>
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"""
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self.name = name
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self.source = source
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self.values = values
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self.distance = distance
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self.got_values_flag = bool(values)
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# initialize .examples from string or list or data directory
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if isinstance(examples, str):
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self.examples = parse_csv(examples)
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elif examples is None:
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self.examples = parse_csv(open_data(name + '.csv').read())
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else:
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self.examples = examples
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# attrs are the indices of examples, unless otherwise stated.
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if self.examples is not None and attrs is None:
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attrs = list(range(len(self.examples[0])))
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self.attrs = attrs
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# initialize .attr_names from string, list, or by default
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if isinstance(attr_names, str):
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self.attr_names = attr_names.split()
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else:
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self.attr_names = attr_names or attrs
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self.set_problem(target, inputs=inputs, exclude=exclude)
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def set_problem(self, target, inputs=None, exclude=()):
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"""
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Set (or change) the target and/or inputs.
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This way, one DataSet can be used multiple ways. inputs, if specified,
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is a list of attributes, or specify exclude as a list of attributes
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to not use in inputs. Attributes can be -n .. n, or an attr_name.
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Also computes the list of possible values, if that wasn't done yet.
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"""
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self.target = self.attr_num(target)
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exclude = list(map(self.attr_num, exclude))
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if inputs:
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self.inputs = remove_all(self.target, inputs)
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else:
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self.inputs = [a for a in self.attrs if a != self.target and a not in exclude]
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if not self.values:
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self.update_values()
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self.check_me()
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def check_me(self):
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"""Check that my fields make sense."""
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assert len(self.attr_names) == len(self.attrs)
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assert self.target in self.attrs
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assert self.target not in self.inputs
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assert set(self.inputs).issubset(set(self.attrs))
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if self.got_values_flag:
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# only check if values are provided while initializing DataSet
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list(map(self.check_example, self.examples))
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def add_example(self, example):
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"""Add an example to the list of examples, checking it first."""
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self.check_example(example)
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self.examples.append(example)
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def check_example(self, example):
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"""Raise ValueError if example has any invalid values."""
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if self.values:
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for a in self.attrs:
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if example[a] not in self.values[a]:
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raise ValueError('Bad value {} for attribute {} in {}'
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.format(example[a], self.attr_names[a], example))
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def attr_num(self, attr):
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"""Returns the number used for attr, which can be a name, or -n .. n-1."""
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if isinstance(attr, str):
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return self.attr_names.index(attr)
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elif attr < 0:
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return len(self.attrs) + attr
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else:
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return attr
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def update_values(self):
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self.values = list(map(unique, zip(*self.examples)))
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def sanitize(self, example):
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"""Return a copy of example, with non-input attributes replaced by None."""
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return [attr_i if i in self.inputs else None for i, attr_i in enumerate(example)][:-1]
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def classes_to_numbers(self, classes=None):
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"""Converts class names to numbers."""
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if not classes:
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# if classes were not given, extract them from values
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classes = sorted(self.values[self.target])
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for item in self.examples:
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item[self.target] = classes.index(item[self.target])
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def remove_examples(self, value=''):
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"""Remove examples that contain given value."""
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self.examples = [x for x in self.examples if value not in x]
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self.update_values()
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def split_values_by_classes(self):
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"""Split values into buckets according to their class."""
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buckets = defaultdict(lambda: [])
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target_names = self.values[self.target]
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for v in self.examples:
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item = [a for a in v if a not in target_names] # remove target from item
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buckets[v[self.target]].append(item) # add item to bucket of its class
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return buckets
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def find_means_and_deviations(self):
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"""
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Finds the means and standard deviations of self.dataset.
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means : a dictionary for each class/target. Holds a list of the means
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of the features for the class.
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deviations: a dictionary for each class/target. Holds a list of the sample
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standard deviations of the features for the class.
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"""
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target_names = self.values[self.target]
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feature_numbers = len(self.inputs)
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item_buckets = self.split_values_by_classes()
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means = defaultdict(lambda: [0] * feature_numbers)
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deviations = defaultdict(lambda: [0] * feature_numbers)
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for t in target_names:
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# find all the item feature values for item in class t
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features = [[] for _ in range(feature_numbers)]
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for item in item_buckets[t]:
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for i in range(feature_numbers):
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features[i].append(item[i])
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# calculate means and deviations fo the class
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for i in range(feature_numbers):
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means[t][i] = mean(features[i])
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deviations[t][i] = stdev(features[i])
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return means, deviations
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def __repr__(self):
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return '<DataSet({}): {:d} examples, {:d} attributes>'.format(self.name, len(self.examples), len(self.attrs))
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