数据挖掘的特征介绍和处理方法介绍

青旅半醒 2021-11-01 11:03 617阅读 0赞

** 一、特征工程**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70][]

二、数据清洗：

1、数据样本抽样

2、异常值（空值）处理

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 1][]

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![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 3][]

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在特征预处理的过程中，进行数据标注是非常重要的，比如我们想要预测明天下雨不下雨，那么这个时候我们得到的数据中，需要对关于我们预测的结果的数据进行标注，也就是下雨不下雨进行标注。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 6][]

上图是一个hr的人力资源的分析图，我们用这个数据会去预测员工是否离职。 并且建立模型，得出什么样的人会离职。

而我们的labe标注在left上面。属性为1为离职，属性为0代表不离职。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 7][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 8][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 9][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 10][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 11][]

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**特征变换：对指化，就是对特征进行对数化和指数化。**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 13][]

先对特征进行指数化，然后再进行归一化（softmax）。

** 对特征进行对数化：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 14][]

数据离散化：就是将连续数据变成离散数据的过程

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 15][]

1.  方法就是分箱技术：等频分箱，等距分箱
2.  朴素贝叶斯算法：需要的数据就是离散的

### **                                                                       分箱技术：** ###

**根据深度和宽度对数据进行分箱**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 16][]

第一个是等深分箱，和等距分箱的实践![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 17][]

归一化是数据在\[0,1\]之间：![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 18][]

** 正规化：用在每个对象的各个特征的表示最多**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 19][]

** 用python操作正规化：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 20][]

根据上面的公式得出的正规化的数据

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 21][]

*** 注意下面的是 L1,L2的正规化。***

from sklearn.preprocessing import Normalizer
    import numpy  as np
    #正规化实际上是对行进行正规化的
    
    x = Normalizer(norm="l1").fit_transform(np.array([1,1,3,-1,2]).reshape(-1,1))
    print(x)
    b = Normalizer(norm="l2").fit_transform(np.array([[1,1,3,-1,2]]))
    print(b)

正规化的结果如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 22][]

### *** 特征降维：*** ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 23][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 24][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 25][]

** 用python操作lda的实现过程**

import  numpy as np
    from sklearn.discriminant_analysis import LinearDiscriminantAnalysis
    X = np.array([[-1,-1],[-2,-1],[-3,-2],[1,1],[2,1],[3,2]])
    Y = np.array([1,1,1,2,2,2])
    m_lda = LinearDiscriminantAnalysis(n_components=1).fit_transform(X,Y)
    print(m_lda)

lda实现结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQxNDc5NDY0_size_16_color_FFFFFF_t_70 26][]

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