import numpy as np
 
#Fancy Indexing
x = np.arange(16)
np.random.shuffle(x)
print(x) #打印所有的元素
 
 
print(x[2])#獲取某個元素的值
print(x[1:3])#切片
print(x[3:9:2])#指定間距切片
 
index = [2,4,7,9] #索引數(shù)組
print(x[index])#獲取索引數(shù)組中的元素的值
 
ind = np.array([[0,2],[1,4]]) #索引二維數(shù)組
print(x[ind])##獲取索引二維數(shù)組中的元素的值
 
print("---------------------")
 
X = x.reshape(4,-1)
print(X)
 
ind1 = np.array([1,3]) #行的索引
ind2 = np.array([2,0]) #列的索引
print(X[ind1,ind2])
 
print(X[:-2,ind2])
 
bool_index = [True,False,True,False] #True就取當前列，F(xiàn)alse就不取
print(X[:-1,bool_index])

x = np.arange(16) 
x[3] # 3
x[3:9] # array([3, 4, 5, 6, 7, 8])
x[3:9:2] # array([3, 5, 7])
[x[3], x[5], x[7]] # [3, 5, 7]
ind = [3, 5, 7] 
x[ind]  # array([3, 5, 7])
ind = np.array([[0, 2], [1, 3]]) 
x[ind] 
"""
array([[0, 2],
    [1, 3]])
"""

X = x.reshape(4, -1) 
"""
array([[ 0, 1, 2, 3],
    [ 4, 5, 6, 7],
    [ 8, 9, 10, 11],
    [12, 13, 14, 15]])
"""
row = np.array([0, 1, 2]) 
col = np.array([1, 2, 3])
# 1行2列，2行3列，3行4列
X[row, col]  # array([ 1, 6, 11])
# 前2行 2,3,4列
X[:2, col] 
"""
array([[1, 2, 3],
    [5, 6, 7]])
"""
col = [True, False, True, True] 
X[0, col]  # array([0, 2, 3])

import numpy as np
 
x = np.arange(16)
print(x)
 
print(x < 3) #返回的是bool數(shù)組
 
print(x == 3)
 
print(x != 3)
 
print(x * 4 == 24 - 4 * x)
 
 
 
print(x + 1)
 
print(x * 2)
 
print(x / 4)
 
print(x - 10)
 
print(np.sum(x<3))#返回小于3的元素個數(shù)
 
print(np.any(x==0)) #只要向量x中有等于0的就返回true
 
print(np.all(x==0)) #只有向量x中全部等于0才返回true
 
print(x[x<5]) #因為x<5返回的是bool數(shù)組，我們?nèi)rue的元素的值
 
 
#二維的同樣支持
print("----------------------")
X = x.reshape(4,-1)
 
print(X)
print(X<3)
print(x == 3)
print(np.sum(X<4))
print(np.count_nonzero(X<5)) #返回X中小于5的不等于0的個數(shù)
print(np.any(X==0)) #只要向量x中有等于0的就返回true
 
print(np.all(X==0)) #只有向量x中全部等于0才返回true
 
print(np.sum(X<4,axis=1))#沿著列的方向，計算每行小于4的個數(shù)
 
print(np.sum((X>3)&(X<10))) #計算X中大于3并且小于10的個數(shù)
 
print(np.sum(~(X==0))) #計算X中不等于0的個數(shù)
 
print(X[X[:,3]%3==0,:]) #因為X[:,3]%3==0返回的是一個向量，元素為true，false，false，true，所以最后取第一行和最后一行