使用 NumPy 导入平面文件

Python 数据导入入门

Hugo Bowne-Anderson

Data Scientist at DataCamp

为什么用 NumPy？

NumPy 数组：存储数值数据的标准

ch_1_3.003.png

为什么用 NumPy？

NumPy 数组：存储数值数据的标准
其他包的基础：如 scikit-learn
loadtxt()
genfromtxt()

使用 NumPy 导入平面文件

import numpy as np
filename = 'MNIST.txt'
data = np.loadtxt(filename, delimiter=',')
data

[[   0.    0.    0.    0.    0.]
 [  86.  250.  254.  254.  254.]
 [   0.    0.    0.    9.  254.]
 ..., 
 [   0.    0.    0.    0.    0.]
 [   0.    0.    0.    0.    0.]
 [   0.    0.    0.    0.    0.]]

自定义 NumPy 导入

import numpy as np
filename = 'MNIST_header.txt'
data = np.loadtxt(filename, delimiter=',', skiprows=1)
print(data)

[[   0.    0.    0.    0.    0.]
 [  86.  250.  254.  254.  254.]
 [   0.    0.    0.    9.  254.]
 ..., 
 [   0.    0.    0.    0.    0.]
 [   0.    0.    0.    0.    0.]
 [   0.    0.    0.    0.    0.]]

skiprows：要跳过的行数（不是索引）

自定义 NumPy 导入

import numpy as np
filename = 'MNIST_header.txt'
data = np.loadtxt(filename, delimiter=',', skiprows=1, usecols=[0, 2])
print(data)

[[   0.    0.]
 [  86.  254.]
 [   0.    0.]
 ..., 
 [   0.    0.]
 [   0.    0.]
 [   0.    0.]]

usecols：要保留的列索引列表

自定义 NumPy 导入

data = np.loadtxt(filename, delimiter=',', dtype=str)

混合数据类型

titanic.csv

                        Name      Sex  Cabin   Fare
     Braund, Mr. Owen Harris     male    NaN    7.3
  Cumings, Mrs. John Bradley   female    C85   71.3
      Heikkinen, Miss. Laina   female    NaN    8.0
Futrelle, Mrs. Jacques Heath   female   C123   53.1
    Allen, Mr. William Henry     male    NaN   8.05

¹ 来源：Kaggle

混合数据类型

titanic.csv

                        Name      Sex  Cabin   Fare
     Braund, Mr. Owen Harris     male    NaN    7.3
  Cumings, Mrs. John Bradley   female    C85   71.3
      Heikkinen, Miss. Laina   female    NaN    8.0
Futrelle, Mrs. Jacques Heath   female   C123   53.1
    Allen, Mr. William Henry     male    NaN   8.05
               ^                                 ^
            strings                           floats

¹ 来源：Kaggle

Vamos praticar!

Python 数据导入入门