numpy 入门


Author: yifei / Created: June 23, 2018, 10:44 a.m. / Modified: June 23, 2018, 10:45 a.m. / Edit

From Python to Numpy

http://www.labri.fr/perso/nrougier/from-python-to-numpy/

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Numpy is a very powerful library and you can make wonders with it but, most of the time, this comes at the price of readability. If you don't comment your code at the time of writing, you won't be able to tell what a function is doing after a few weeks (or possibly days).

np.array

np.array is the basic structure is numpy. It's a n-dimension array

directly from a python list or lists

print(type(a)) # Prints "" print(a.shape) # Prints "(3,)" print(a[0], a[1], a[2]) # Prints "1 2 3" a[0] = 5 # Change an element of the array print(a) # Prints "[5, 2, 3]" b = np.array([[1,2,3],[4,5,6]]) # Create a rank 2 array print(b.shape) # Prints "(2, 3)" print(b[0, 0], b[0, 1], b[1, 0]) # Prints "1 2 4" Numpy also provides many functions to create arrays: import numpy as np a = np.zeros((2,2)) # Create an array of all zeros print(a) # Prints "[[ 0. 0.] # [ 0. 0.]]" b = np.ones((1,2)) # Create an array of all ones print(b) # Prints "[[ 1. 1.]]" c = np.full((2,2), 7) # Create a constant array print(c) # Prints "[[ 7. 7.] # [ 7. 7.]]" d = np.eye(2) # Create a 2x2 identity matrix print(d) # Prints "[[ 1. 0.] # [ 0. 1.]]" e = np.random.random((2,2)) # Create an array filled with random values print(e) # Might print "[[ 0.91940167 0.08143941] # [ 0.68744134 0.87236687]]"


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