Platte bestanden importeren met NumPy

Introductie tot data importeren in Python

Hugo Bowne-Anderson

Data Scientist at DataCamp

Waarom NumPy?

NumPy-arrays: standaard voor numerieke data

ch_1_3.003.png

Waarom NumPy?

NumPy-arrays: standaard voor numerieke data
Essentieel voor andere pakketten, bijv. scikit-learn
loadtxt()
genfromtxt()

Platte bestanden importeren met 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.]]

Je NumPy-import aanpassen

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: hoeveel rijen (niet indexen) je wilt overslaan

Je NumPy-import aanpassen

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: lijst met indexen van kolommen die je wilt behouden

Je NumPy-import aanpassen

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

Gemengde datatypes

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 Bron: Kaggle

Gemengde datatypes

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 Bron: Kaggle

Laten we oefenen!

Introductie tot data importeren in Python