numpy

import numpy as np

Create an array of ones

n = np.ones((3,4))

print("np.ones: ",n)

Create an array of zeros

n=np.zeros((2,3,4),dtype=np.int16) print("np.zeros: ",n)

Create an array with random values

n=np.random.random((2,2)) print("random.random: ",n)

Create an empty array

n=np.empty((3,2)) print("empty: ",n)

Create a full array

n=np.full((2,2),7) print("full: ",n)

Create an array of evenly-spaced values

n=np.arange(10,25,5) print("arange: ",n)

Create an array of evenly-spaced values

n=np.linspace(0,2,9) print("linspace: ",n)

n = np.eye(5) print("np.eye: ",n)

n = np.identity(5) print("np.identity: ",n)

Import

nHIGH=np.eye(500) np.save('/home/silvio/testg',nHIGH) np.savetxt('/home/silvio/testg.txt',nHIGH) np.savez('/home/silvio/testH',nHIGH) np.savez_compressed('/home/silvio/testH-c',nHIGH)

!ls -l /home/silvio/testg.npy !ls -l /home/silvio/testH.npz !ls -l /home/silvio/testH-c.npz !cat /home/silvio/testg.npy

my_array2 = np.loadtxt('/home/silvio/testg.txt') print("my_array2: ",my_array2)

my_array2 = np.load('/home/silvio/testg.npy') #, skip_header=1, filling_values=-999)

print("my_array2: ",my_array2)

my_array2 = np.load('/home/silvio/testH-c.npz') #, skip_header=1, filling_values=-999)

print("my_array2: ",my_array2) print("my_array2: ",my_array2.files) print("my_array2: ",my_array2['arr_0']) my_array=np.full((12,12),70)

Print the number of my_array's dimensions

print(my_array.ndim)

Print the number of my_array's elements

print(my_array.size)

Print information about my_array's memory layout

print(my_array.flags)

Print the length of one array element in bytes

print(my_array.itemsize)

Print the total consumed bytes by my_array's elements

print(my_array.nbytes) np.savez('my_array',my_array)

x=np.random.random((3,4)) y=np.random.random((5,1,4))

Add x and y

res=np.add(x,y) print('res: ',res)

res2=res.sum() print('res2: ',res2)

my_2d_array=np.random.random((4,4))

Select the element at row 1 column 2

print(my_2d_array[1][2])

Select the element at row 1 column 2

print(my_2d_array[1,2])

Concatenate arrays:

• grid = np.array([[1, 2, 3],[4, 5, 6]])

• grid2 = np.array([[10, 20, 30],[40, 50, 60]])

• np.concatenate([grid, grid2])

• x = np.array([1, 2, 3])

• grid = np.array([[9, 8, 7],[6, 5, 4]])

Vertically stack the arrays

• np.vstack([x, grid])

Horizontally stack the arrays

• y = np.array([[99],[99]])
• np.hstack([grid, y])

Split

• array([[ 0, 1, 2, 3],[ 4, 5, 6, 7],[ 8, 9, 10, 11],[12, 13, 14, 15]])
• upper, lower = np.vsplit(grid, [2])
• print(upper)
• print(lower)

Exercícios:

• Crie um array com 10 elementos usando a função arange

• Transforme esse array de 1D (1x10) para 2D (2x5) usando a função reshape

• Crie duas matrizes bidimensionais com valores aleatórios

• calcule a transposta de cada matriz

• multiplique as duas matrizes

• Salve as matrizes de entrada e a de saída em arquivos. Qual o tamanho dos arquivos gerados?

• Crie duas bidimensionais matrizes com valores aleatórios e gere uma única matriz combinando linha a linha

Referências:

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