<必學！Python資料科學.機器學習最強套件>
- [ ] CH5，努力推進中
> 5-2的練習1

#
#
#start

import numpy as np

alfa = np.random.randn(5)
beta = np.random.randn(5)

print("alfa:", alfa)
print("beta:", beta)

> 5-2的練習2

#
#
#start

import numpy as np

alfa = np.random.randn(5)
beta = np.random.randn(5)

print("alfa:", alfa)
print("beta:", beta)


np.random.seed(0)
alfa = np.random.randn(5)

np.random.seed(0)
beta = np.random.randn(5)

print("alfa:", alfa)
print("beta:", beta)

> 5-2的練習3

import numpy as np

arr1 = np.random.randint(0,11,(5,2))
print('arr1:')
print(arr1)

arr2 = np.random.rand(3)
print('arr2:')
print(arr2)

> 5-2的練習4
> 我是紅軍球迷，練習拿了球員挑了11人
> 我想應該要分前鋒/中場/後衛/門將來隨機挑11人吧？
> 要不然會重複，呵呵

#
#
#start

import numpy as np
np.random.seed(0)
player = ['Salah', 'Jota', 'Gakpo','Darwin','Diaz','Doak','Szoboslai','MacAlister',
          'Eliott','Jones','Gravenberch','Endo','Robertson','Tsimikas','Virgil','Matip','Konate',
          'Quansa','Alexander-Arnold','Gomez','Alisson','Kellerher']

print(np.random.choice(player,11))

5-2練習5，複製陣列

#
#
#start

import numpy as np
print('------W/O copy-----')
arr1 = np.array([1,2,3,4,5])
print('arr1:'+str(arr1))

arr2 = arr1
arr2[0] = 100
print('arr2:'+str(arr1))
print('arr1:'+str(arr2))


print('-----W/COPY-----')
arr1 = np.array([1,2,3,4,5])
print('arr1:'+str(arr1))

arr2 = arr1.copy()

arr2[0] = 100

print('arr1:'+str(arr1))
print('arr2:'+str(arr2))
print('arr1:'+str(arr1))

5-2練習6，Slicing

#
#
#start

import numpy as np
arr = np.arange(10)

print(arr)

arr[0:3] = 1

print(arr)

5-2練習7，布林

#
#
#start

import numpy as np
arr = np.arange(10)

new_arr = arr<5

print(arr)
print(new_arr)
print(arr[new_arr])

5-2練習8，陣列四則運算

#
#
#start

#w/python
storages = [1,2,3,4]

new_storages = []
for n in storages:
    n += n
    new_storages.append(n)

print(new_storages)

#w/numpy
import numpy as np
storages = np.array([1,2,3,4])

storages += storages
print(storages)

5-2練習9，續陣列四則運算

#
#
#start

import numpy as np
arr_1 = np.array([2,4,6,8,10])
arr_2 = np.array([1,3,5,7,9])

#addition
print('arr_1 + arr_2:')
print(arr_1 + arr_2)
print('--------------------------')

#subtraction
print('arr_1 - arr_2:')
print(arr_1 - arr_2)
print('--------------------------')

#mutiplication, cupid
print('arr_1 ** 3:')
print(arr_1 ** 3)
print('--------------------------')

#division
print('arr_1 / arr_2:')
print(arr_1 / arr_2)
print('--------------------------')

5-2練習10，絕對值平方根自然對數

#
#
#start

import numpy as np
arr = np.array([4,9,16,-4,20])
print(arr)

arr_abs = np.abs(arr)
print('絕對值：', arr_abs)

print('自然對數：', np.exp(arr_abs))
print('平方根：', np.sqrt(arr_abs))