Importera flatfiler med NumPy

Introduktion till dataimport i Python

Hugo Bowne-Anderson

Data Scientist at DataCamp

Varför NumPy?

NumPy-arrayer: standard för att lagra numeriska data

ch_1_3.003.png

Varför NumPy?

NumPy-arrayer: standard för att lagra numeriska data
Krävs av andra paket, t.ex. scikit-learn
loadtxt()
genfromtxt()

Importera flatfiler med NumPy

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.]]

Anpassa din NumPy-import

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: antal rader (inte index) som ska hoppas över

Anpassa din NumPy-import

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: lista med index för de kolumner du vill behålla

Anpassa din NumPy-import

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

Blandade datatyper

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 Källa: Kaggle

Blandade datatyper

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
               ^                                 ^
            strängar                          floats

¹ Källa: Kaggle

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Introduktion till dataimport i Python