Numpy

Initialize

0으로 초기화

init_zero.py

import numpy as np

a = np.zeros(5)
b = np.zeros((5,4))

print('a = ', a)
print('********************')
print('b = ', b)
print('********************')

print('b.shape = ', b.shape)
print('********************')
print('b.ndim', b.ndim) #len(b.shape)
print('********************')
print('b.size = ', b.size)

Result

a =  [0. 0. 0. 0. 0.]
********************
b =  [[0. 0. 0. 0.]
 [0. 0. 0. 0.]
 [0. 0. 0. 0.]
 [0. 0. 0. 0.]
 [0. 0. 0. 0.]]
********************
b.shape =  (5, 4)
********************
b.ndim 2
********************
b.size =  20

1로 초기화

init_one.py

import numpy as np

a = np.ones(5)
b = np.ones((5,4))

print('a = ', a)
print('********************')
print('b = ', b)

Result

a =  [1. 1. 1. 1. 1.]
********************
b =  [[1. 1. 1. 1.]
 [1. 1. 1. 1.]
 [1. 1. 1. 1.]
 [1. 1. 1. 1.]
 [1. 1. 1. 1.]]

지정한 수로 초기화

init_sel.py

import numpy as np

a = np.full(5, 42)
b = np.full((5,4), 21)

print('a = ', a)
print('********************')
print('b = ', b)

Result

a =  [42 42 42 42 42]
********************
b =  [[21 21 21 21]
 [21 21 21 21]
 [21 21 21 21]
 [21 21 21 21]
 [21 21 21 21]]

List로 초기화

init_list.py

import numpy as np

a = np.array([10, 10, 10])
b = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

print('a = ', a)
print('********************')
print('b = ', b)
print('********************')
print('Type of b = ', type(b))

Result

a =  [10 10 10]
********************
b =  [[1 2 3]
 [4 5 6]
 [7 8 9]]
********************
Type of b =  <class 'numpy.ndarray'>

범위로 초기화

init_ran.py

import numpy as np

a = np.arange(0, np.pi, 0.4) #간격의 크기
b = np.linspace(0, np.pi, 6) #간격의 수

print('a = ', a)
print('********************')
print('b = ', b)

Result

a =  [0.  0.4 0.8 1.2 1.6 2.  2.4 2.8]
********************
b =  [0.         0.62831853 1.25663706 1.88495559 2.51327412 3.14159265]

함수로 초기화

init_func.py

import numpy as np

def init_function_2(x, y):
    return x * y

def init_function_3(z, x, y):
    return x * y + z

a = np.fromfunction(init_function_2, (5, 5))
b = np.fromfunction(init_function_3, (2, 5, 5))

print('a = ', a)
print('********************')
print('b = ', b)

Result

a =  [[ 0.  0.  0.  0.  0.]
 [ 0.  1.  2.  3.  4.]
 [ 0.  2.  4.  6.  8.]
 [ 0.  3.  6.  9. 12.]
 [ 0.  4.  8. 12. 16.]]
********************
b =  [[[ 0.  0.  0.  0.  0.]
  [ 0.  1.  2.  3.  4.]
  [ 0.  2.  4.  6.  8.]
  [ 0.  3.  6.  9. 12.]
  [ 0.  4.  8. 12. 16.]]

 [[ 1.  1.  1.  1.  1.]
  [ 1.  2.  3.  4.  5.]
  [ 1.  3.  5.  7.  9.]
  [ 1.  4.  7. 10. 13.]
  [ 1.  5.  9. 13. 17.]]]

데이터 형 지정

data_type.py

import numpy as np

a = np.arange(1, 5, dtype = np.uint8)
b = np.array([[1, 2, 3], [4, 5, 6]], dtype = np.complex64)

print('a = ', a)
print('********************')
print('b = ', b)

Result

a =  [1 2 3 4]
********************
b =  [[1.+0.j 2.+0.j 3.+0.j]
 [4.+0.j 5.+0.j 6.+0.j]]

---

Methods of np.ndarray

Math Function

method_st.py

import numpy as np

a = np.array([[1, 2, 3], [4, 5, 6]], dtype = np.uint8)

for func in (a.min, a.max, a.sum, a.prod, a.std, a.var):
    print(func.__name__, "=", func())

axis = n과 같이 축을 설정하여 계산 가능

Result

min = 1
max = 6
sum = 21
prod = 720
std = 1.707825127659933
var = 2.9166666666666665

Universal Function

method_un.py

import numpy as np

a = np.array([[1, 2, 3], [4, 5, 6]], dtype = np.uint8)

for func in (np.square, np.abs, np.sqrt, np.exp, np.log, np.sign, np.ceil, np.modf, np.isnan, np.cos):
    print(func.__name__, "=", func(a))

Result

square = [[ 1  4  9]
 [16 25 36]]
absolute = [[1 2 3]
 [4 5 6]]
sqrt = [[1.    1.414 1.732]
 [2.    2.236 2.45 ]]
exp = [[  2.719   7.39   20.08 ]
 [ 54.6   148.4   403.5  ]]
log = [[0.     0.6934 1.099 ]
 [1.387  1.609  1.792 ]]
sign = [[1 1 1]
 [1 1 1]]
ceil = [[1. 2. 3.]
 [4. 5. 6.]]
modf = (array([[0., 0., 0.],
       [0., 0., 0.]], dtype=float16), array([[1., 2., 3.],
       [4., 5., 6.]], dtype=float16))
isnan = [[False False False]
 [False False False]]
cos = [[ 0.5405 -0.4163 -0.99  ]
 [-0.654   0.2837  0.96  ]]