数据挖掘实践指南读书笔记7
2016-11-16 本文已影响51人
hainingwyx
写在之前
本书涉及的源程序和数据都可以在以下网站中找到：http://guidetodatamining.com/
这本书理论比较简单，书中错误较少，动手锻炼较多，如果每个代码都自己写出来，收获不少。总结：适合入门。
欢迎转载，转载请注明出处，如有问题欢迎指正。
合集地址：https://www.zybuluo.com/hainingwyx/note/559139
聚类--群组发现
层次聚类：每次迭代将最相似的两个簇合并，不断重复直至只有一个簇。两个簇距离计算方法不一样，聚类的方法就不一样，合并的过程也不一样。
- 单连接聚类：两个簇的距离定义为一个簇的所有成员到另一个簇的所有成员最短的距离
- 全连接聚类：两个簇的距离定义为一个簇的所有成员到另一个簇的所有成员最长的距离
- 平均连接聚类：两个簇的距离定义为一个簇的所有成员到另一个簇的所有成员的平均距离
常规队列：先进先出
优先级队列：去除次序基于队列元素的关联权重，数值越小先去除。
# 从队列中获得数据的最小值
from Queue import PriorityQueue
singersQueue = PriorityQueue()
singersQueue.put((16, 'Suzaka'))
singersQueue.put((14, 'Yui'))
singersQueue.put((15, 'Moa'))
print singersQueue.get()
print singersQueue.get()
print singersQueue.get()
class hClusterer:
""" this clusterer assumes that the first column of the data is a label
not used in the clustering. The other columns contain numeric data"""
def __init__(self, filename):
file = open(filename)
self.data = {}
self.counter = 0
self.queue = PriorityQueue()
lines = file.readlines()
file.close()
header = lines[0].split(',')
self.cols = len(header)
self.data = [[] for i in range(len(header))]
for line in lines[1:]:
cells = line.split(',')
toggle = 0
# self.data [['Border Collie',...], [20.0,...], [45.0,...]]
for cell in range(self.cols):
if toggle == 0:
self.data[cell].append(cells[cell])
toggle = 1
else:
self.data[cell].append(float(cells[cell]))
# now normalize number columns (that is, skip the first column)
for i in range(1, self.cols):
self.data[i] = normalizeColumn(self.data[i])
###
### I have read in the data and normalized the
### columns. Now for each element i in the data, I am going to
### 1. compute the Euclidean Distance from element i to all the
### other elements. This data will be placed in neighbors,
### which is a Python dictionary. Let's say i = 1, and I am
### computing the distance to the neighbor j and let's say j
### is 2. The neighbors dictionary for i will look like
### {2: ((1,2), 1.23), 3: ((1, 3), 2.3)... }
###
### 2. find the closest neighbor
###
### 3. place the element on a priority queue, called simply queue,
### based on the distance to the nearest neighbor (and a counter
### used to break ties.
# now push distances on queue
rows = len(self.data[0])
for i in range(rows):
minDistance = 99999
nearestNeighbor = 0
neighbors = {} #存储所有邻居的对和距离
for j in range(rows):
if i != j:
dist = self.distance(i, j)
if i < j:
pair = (i,j)
else:
pair = (j,i)
neighbors[j] = (pair, dist)
if dist < minDistance:
minDistance = dist
nearestNeighbor = j
# nearestNum = j
# create nearest Pair
if i < nearestNeighbor:
nearestPair = (i, nearestNeighbor)
else:
nearestPair = (nearestNeighbor, i)
# put instance on priority queue
self.queue.put((minDistance, self.counter,
[[self.data[0][i]], nearestPair, neighbors]))
self.counter += 1 #存储对象的数量，先后顺序
def distance(self, i, j):
sumSquares = 0
for k in range(1, self.cols):
sumSquares += (self.data[k][i] - self.data[k][j])**2
return math.sqrt(sumSquares)
def cluster(self):
done = False
while not done:
# 依据 minDistance 取出当前最小距离的对象,应该是两对距离。
topOne = self.queue.get()
nearestPair = topOne[2][1]
if not self.queue.empty():
nextOne = self.queue.get()
nearPair = nextOne[2][1] #当等距离时，不一定一样的
tmp = []
##
## I have just popped two elements off the queue,
## topOne and nextOne. I need to check whether nextOne
## is topOne's nearest neighbor and vice versa.
## If not, I will pop another element off the queue
## until I find topOne's nearest neighbor. That is what
## this while loop does.
##
# 处理等距离的情况
while nearPair != nearestPair:
tmp.append((nextOne[0], self.counter, nextOne[2]))
self.counter += 1
nextOne = self.queue.get()
nearPair = nextOne[2][1]
##
## this for loop pushes the elements I popped off in the
## above while loop.
## 放回等距离不配对的对象
for item in tmp:
self.queue.put(item)
if len(topOne[2][0]) == 1:
item1 = topOne[2][0][0]
else:
item1 = topOne[2][0]
if len(nextOne[2][0]) == 1:
item2 = nextOne[2][0][0]
else:
item2 = nextOne[2][0]
## curCluster is, perhaps obviously, the new cluster
## which combines cluster item1 with cluster item2.
curCluster = (item1, item2)
## Now I am doing two things. First, finding the nearest
## neighbor to this new cluster. Second, building a new
## neighbors list by merging the neighbors lists of item1
## and item2. If the distance between item1 and element 23
## is 2 and the distance betweeen item2 and element 23 is 4
## the distance between element 23 and the new cluster will
## be 2 (i.e., the shortest distance).
##
minDistance = 99999
nearestPair = ()
#nearestNeighbor = ''
merged = {}
nNeighbors = nextOne[2][2] #所有的邻居对和距离
for (key, value) in topOne[2][2].items():
if key in nNeighbors: #只剩下最后一个的时候，不成立
if nNeighbors[key][1] < value[1]:
dist = nNeighbors[key]
else:
dist = value
if dist[1] < minDistance:
minDistance = dist[1]
nearestPair = dist[0] #这里的对比较特别，只去了其中一个点
#nearestNeighbor = key
merged[key] = dist
if merged == {}:
return curCluster#返回元祖对，用来建立树
else:
self.queue.put( (minDistance, self.counter,
[curCluster, nearestPair, merged]))
self.counter += 1
KMeans
这个算法和爬山法类似，不能保证最后能够找到最有的划分簇。因为算法一开始选择的是随机中心点的集合，所以只能确保找到局部最有划分簇。
误差平方和(sum of squared error,简称SSE)：度量某个簇集合的质量。
import math
import random
"""
Implementation of the K-means algorithm
for the book A Programmer's Guide to Data Mining"
http://www.guidetodatamining.com
"""
def getMedian(alist):
"""get median of list"""
tmp = list(alist)
tmp.sort()
alen = len(tmp)
if (alen % 2) == 1:
return tmp[alen // 2]
else:
return (tmp[alen // 2] + tmp[(alen // 2) - 1]) / 2
def normalizeColumn(column):
"""normalize the values of a column using Modified Standard Score
that is (each value - median) / (absolute standard deviation)"""
median = getMedian(column)
asd = sum([abs(x - median) for x in column]) / len(column)
result = [(x - median) / asd for x in column]
return result
class kClusterer:
""" Implementation of kMeans Clustering
This clusterer assumes that the first column of the data is a label
not used in the clustering. The other columns contain numeric data
"""
def __init__(self, filename, k):
""" k is the number of clusters to make
This init method:
1. reads the data from the file named filename
2. stores that data by column in self.data
3. normalizes the data using Modified Standard Score
4. randomly selects the initial centroids
5. assigns points to clusters associated with those centroids
"""
file = open(filename)
self.data = {}
self.k = k
self.counter = 0
self.iterationNumber = 0
# used to keep track of % of points that change cluster membership
# in an iteration
self.pointsChanged = 0
# Sum of Squared Error
self.sse = 0
#
# read data from file
#
lines = file.readlines()
file.close()
header = lines[0].split(',')
self.cols = len(header)
self.data = [[] for i in range(len(header))]
# we are storing the data by column.
# For example, self.data[0] is the data from column 0.
# self.data[0][10] is the column 0 value of item 10.
for line in lines[1:]:
cells = line.split(',')
toggle = 0
for cell in range(self.cols):
if toggle == 0:
self.data[cell].append(cells[cell])
toggle = 1
else:
self.data[cell].append(float(cells[cell]))
self.datasize = len(self.data[1])
self.memberOf = [-1 for x in range(len(self.data[1]))]
#
# now normalize number columns
#
for i in range(1, self.cols):
self.data[i] = normalizeColumn(self.data[i])
# select random centroids from existing points
random.seed()
#sample(seq, n) 从序列seq中选择n个随机且独立的元素
self.centroids = [[self.data[i][r] for i in range(1, len(self.data))]
for r in random.sample(range(len(self.data[0])),
self.k)]
self.assignPointsToCluster()
def updateCentroids(self):
"""Using the points in the clusters, determine the centroid
(mean point) of each cluster"""
members = [self.memberOf.count(i) for i in range(len(self.centroids))]#计数列表
#对centroid类的数据的第k列数据 第i个中心点求和，计算平均
self.centroids = [[sum([self.data[k][i]
for i in range(len(self.data[0]))
if self.memberOf[i] == centroid])/members[centroid]
for k in range(1, len(self.data))]
for centroid in range(len(self.centroids))]
def assignPointToCluster(self, i):
""" assign point to cluster based on distance from centroids"""
min = 999999
clusterNum = -1
for centroid in range(self.k):
dist = self.euclideanDistance(i, centroid)
if dist < min:
min = dist
clusterNum = centroid
# here is where I will keep track of changing points
if clusterNum != self.memberOf[i]: #第一次认为全部变动
self.pointsChanged += 1
# add square of distance to running sum of squared error
self.sse += min**2
return clusterNum
def assignPointsToCluster(self):
""" assign each data point to a cluster"""
self.pointsChanged = 0
self.sse = 0
self.memberOf = [self.assignPointToCluster(i)
for i in range(len(self.data[1]))]
def euclideanDistance(self, i, j):
""" compute distance of point i from centroid j"""
sumSquares = 0
for k in range(1, self.cols):
sumSquares += (self.data[k][i] - self.centroids[j][k-1])**2
return math.sqrt(sumSquares)
def kCluster(self):
"""the method that actually performs the clustering
As you can see this method repeatedly
updates the centroids by computing the mean point of each cluster
re-assign the points to clusters based on these new centroids
until the number of points that change cluster membership is less than 1%.
"""
done = False
while not done:
self.iterationNumber += 1
self.updateCentroids()
self.assignPointsToCluster()
#
# we are done if fewer than 1% of the points change clusters
#
if float(self.pointsChanged) / len(self.memberOf) < 0.01:
done = True
print("Final SSE: %f" % self.sse)
def showMembers(self):
"""Display the results"""
for centroid in range(len(self.centroids)):
print ("\n\nClass %i\n========" % centroid)
for name in [self.data[0][i] for i in range(len(self.data[0]))
if self.memberOf[i] == centroid]:
print (name)
##
## RUN THE K-MEANS CLUSTERER ON THE DOG DATA USING K = 3
###
# change the path in the following to match where dogs.csv is on your machine
km = kClusterer('data/dogs.csv', 3)
km.kCluster()
km.showMembers()
K-means++通过修改初始中心点的选择方法改进了由于初始的随机性导致的结果非优的缺点。虽然第一个点选择是随机的，但其他的点则优先选择那些彼此距离很远的点。
选择初始中心点的步骤：
- 从数据点中随机选择第一个中心点
- 重复以下过程，直到选出k个中心点
- 计算每个数据点dp到其最近的中心点的距离D(dp)
- 以正比D(dp)的概率，随机选择一个数据点作为新中心点加入到中心点集合
def selectInitialCentroids(self):
"""implement the k-means++ method of selecting
the set of initial centroids"""
centroids = []
total = 0
# first step is to select a random first centroid
current = random.choice(range(len(self.data[0])))
centroids.append(current)
# loop to select the rest of the centroids, one at a time
for i in range(0, self.k - 1):
# for every point in the data find its distance to
# the closest centroid
weights = [self.distanceToClosestCentroid(x, centroids)
for x in range(len(self.data[0]))]
total = sum(weights)
# instead of raw distances, convert so sum of weight = 1
weights = [x / total for x in weights]
#
# now roll virtual die
num = random.random()
total = 0
x = -1
# the roulette wheel simulation
while total < num:
x += 1
total += weights[x]
centroids.append(x)
self.centroids = [[self.data[i][r] for i in range(1, len(self.data))]
for r in centroids]
def distanceToClosestCentroid(self, point, centroidList):
result = self.eDistance(point, centroidList[0])
for centroid in centroidList[1:]:
distance = self.eDistance(point, centroid)
if distance < result:
result = distance
return result
def eDistance(self, i, j):
""" compute distance of point i from centroid j"""
sumSquares = 0
for k in range(1, self.cols):
sumSquares += (self.data[k][i] - self.data[k][j])**2
return math.sqrt(sumSquares)
