隔离林-了解情节

Question

我是隔离林的入门者，我从此链接中的教程开始：

https://www.kaggle.com/rgaddati/unsupervised-fraud-detection-isolation-forest

我不了解路径长度的第一幅图。棕色是什么意思？

谢谢您的帮助

##All General Import Statements
import pandas as pd
import numpy as np
import math
import random
%matplotlib inline
import random
from matplotlib import pyplot
import os
print(os.listdir("../input"))
class ExNode:
    def __init__(self,size):
        self.size=size

class InNode:
    def __init__(self,left,right,splitAtt,splitVal):
        self.left=left
        self.right=right
        self.splitAtt=splitAtt
        self.splitVal=splitVal

def iForest(X,noOfTrees,sampleSize):
    forest=[]
    hlim=math.ceil(math.log(sampleSize,2))
    for i in range(noOfTrees):
        X_train=df_data.sample(sampleSize)
        forest.append(iTree(X_train,0,hlim))
    return forest

def pathLength(x,Tree,currHeight):
    if isinstance(Tree,ExNode):
        return currHeight
    a=Tree.splitAtt
    if x[a]<Tree.splitVal:
        return pathLength(x,Tree.left,currHeight+1)
    else:
        return pathLength(x,Tree.right,currHeight+1)

df=pd.read_csv("../input/creditcard.csv")
y_true=df['Class']
df_data=df.drop('Class',1)

sampleSize=10000
ifor=iForest(df_data.sample(100000),10,sampleSize) ##Forest of 10 trees

posLenLst=[]
negLenLst=[]

for sim in range(1000):
    ind=random.choice(df_data[y_true==1].index)
    for tree in ifor:
        posLenLst.append(pathLength(df_data.iloc[ind],tree,0))

    ind=random.choice(df_data[y_true==0].index)
    for tree in ifor:
        negLenLst.append(pathLength(df_data.iloc[ind],tree,0))

bins = np.linspace(0,math.ceil(math.log(sampleSize,2)), math.ceil(math.log(sampleSize,2)))

pyplot.figure(figsize=(12,8))
pyplot.hist(posLenLst, bins, alpha=0.5, label='Anomaly')
pyplot.hist(negLenLst, bins, alpha=0.5, label='Normal')
pyplot.xlabel('Path Length')
pyplot.ylabel('Frequency')
pyplot.legend(loc='upper left')

Answer 1

棕色外观喜欢棕褐色和蓝色的混合。所以我认为那是它们重叠的地方。这很明显，因为每个的Alpha为.5

进一步解释：颜色在重叠的地方混合在一起。它绘制蓝色，然后如果也有棕褐色，则将其绘制在顶部。由于这些颜色的Alpha为0.5，而Alpha是透明的，因此这些颜色是混合的。导致它们重叠的地方变成棕色。尝试分别绘制每个图，您会发现它们会重叠。