25.numpy 1

import numpy as np

mylist = list([1,2,3,4])

mylist

[1, 2, 3, 4]

myarray = np.array([1,2,3,4])

myarray

array([1, 2, 3, 4])

new = myarray/2

new

array([0.5, 1. , 1.5, 2. ])

new_list = mylist/2

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-15-182a7d153636> in <module>
----> 1 new_list = mylist/2

TypeError: unsupported operand type(s) for /: 'list' and 'int'

type(myarray)

numpy.ndarray

type(mylist)

list

# Creating an array
import numpy as np
myarray = np.array([1,2,3,4,5,6])
print(myarray)

[1 2 3 4 5 6]

type(myarray)

numpy.ndarray

# 0-Dimensional array
myarray0 = np.array(40)

print(myarray0)

40

type(myarray0)

numpy.ndarray

# 1- Dimension array
myarray1 = np.array([1,2,3])
print(myarray1)

[1 2 3]

# 2- Dimension array
myarray2 = np.array([[1,2,3],[4,5,6],[7,8,9]])
print(myarray2)

[[1 2 3]
 [4 5 6]
 [7 8 9]]

# 3- Dimensional array
myarray3 = np.array([[[1,2],[4,5]],[[1,2],[2,5]]])
print(myarray3)

[[[1 2]
  [4 5]]

 [[1 2]
  [2 5]]]

type(myarray3)

numpy.ndarray

# Dimension of arrays
print(myarray3.ndim)

3

print(myarray2.ndim)

2

print(myarray1.ndim)

1

print(myarray0.ndim)

0

# Higher dimension

myarray = np.array([1,2,3,4,5],ndmin=5)
print(myarray)

[[[[[1 2 3 4 5]]]]]

## Accessing the elements

print(myarray1)

[1 2 3]

myarray1[1]

2

print(myarray2)

[[1 2 3]
 [4 5 6]
 [7 8 9]]

print(myarray2[2, 1])

8

print(myarray1[-1])

3

print(myarray3)

[[[1 2]
  [4 5]]

 [[1 2]
  [2 5]]]

print(myarray3[1, 0, 1])

2

print(myarray3[0,0,1])

2

# Slicing [start:stop:step]

myarray1

array([1, 2, 3])

print(myarray1[1:])

[2 3]

print(myarray1[::-1])

[3 2 1]

print(myarray1[::2])

[1 3]

myarray2

array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])

print(myarray2[0:3,1])

[2 5 8]

print(myarray2[1: ,])

[[4 5 6]
 [7 8 9]]

print(myarray2[ : ,1:])

[[2 3]
 [5 6]
 [8 9]]

print(myarray2[1: , 1: ])

[[5 6]
 [8 9]]

## Special arrays

myarray = np.arange(10)

myarray

array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])

myarray = np.zeros(3)

print(myarray)

[0. 0. 0.]

myarray = np.zeros((2,3))

myarray

array([[0., 0., 0.],
       [0., 0., 0.]])

myarray = np.ones((2,3))

myarray

array([[1., 1., 1.],
       [1., 1., 1.]])

myarray = np.eye(3)

myarray

array([[1., 0., 0.],
       [0., 1., 0.],
       [0., 0., 1.]])

myarray = np.linspace(1,5,10)

myarray

array([1.        , 1.44444444, 1.88888889, 2.33333333, 2.77777778,
       3.22222222, 3.66666667, 4.11111111, 4.55555556, 5.        ])

myarray.ndim

1

myarray = np.linspace(1,10,10)

myarray

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

myarray = np.linspace(1,10,6)

myarray

array([ 1. ,  2.8,  4.6,  6.4,  8.2, 10. ])

# reshaping
myarray = np.eye(4)

myarray

array([[1., 0., 0., 0.],
       [0., 1., 0., 0.],
       [0., 0., 1., 0.],
       [0., 0., 0., 1.]])

myarray.reshape((2,8))

array([[1., 0., 0., 0., 0., 1., 0., 0.],
       [0., 0., 1., 0., 0., 0., 0., 1.]])

myarray.reshape((2,9))

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-116-858813a99177> in <module>
----> 1 myarray.reshape((2,9))

ValueError: cannot reshape array of size 16 into shape (2,9)

myarray.reshape(16)

array([1., 0., 0., 0., 0., 1., 0., 0., 0., 0., 1., 0., 0., 0., 0., 1.])