numpy运算

• numpy的与运算

#numpy's universal function
X
array([[ 0,  1,  2],
       [ 3,  4,  5],
       [ 6,  7,  8],
       [ 9, 10, 11],
       [12, 13, 14]])
X + 1
array([[ 1,  2,  3],
       [ 4,  5,  6],
       [ 7,  8,  9],
       [10, 11, 12],
       [13, 14, 15]])
X * 2
array([[ 0,  2,  4],
       [ 6,  8, 10],
       [12, 14, 16],
       [18, 20, 22],
       [24, 26, 28]])
np.sin(X)
array([[ 0.        ,  0.84147098,  0.90929743],
       [ 0.14112001, -0.7568025 , -0.95892427],
       [-0.2794155 ,  0.6569866 ,  0.98935825],
       [ 0.41211849, -0.54402111, -0.99999021],
       [-0.53657292,  0.42016704,  0.99060736]])

• numpy 中 argsort()

x = np.arange(16)
x
array([ 0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15])
#随机打乱
np.random.shuffle(x)
x
array([ 2, 10,  4, 13,  7, 11,  8, 12,  5,  0,  3,  6, 14,  9, 15,  1])
#argsort   元素从小排序所对应的索引
np.argsort(x)
array([ 9, 15,  0, 10,  2,  8, 11,  4,  6, 13,  1,  5,  7,  3, 12, 14],
          dtype=int64)

• numpy 中的布尔索引

names = np.array(['Bob','Mor','Will','Joe','Mor','Will','Will'])
names
array(['Bob', 'Mor', 'Will', 'Joe', 'Mor', 'Will', 'Will'], dtype='<U4')
#使用np.random 模块的randn   生成一些正态分布的随机数据
data = np.random.randn(7,4)
data
array([[ 0.30878037, -0.4096957 , -0.83750594, -0.97213605],
       [-0.14167727, -0.04756769,  1.97948161, -1.702129  ],
       [-1.16628504, -0.4982823 ,  1.53364224, -1.15853535],
       [-0.11616092,  1.07999647, -0.35885284, -0.84570262],
       [-0.12763289, -1.29314938, -0.80078425, -0.08737958],
       [ 1.45718967, -1.14880644,  0.09459774, -0.25857695],
       [-0.2095555 , -0.53830113,  0.63900549,  0.05845763]])

#假设  每个名字对应data数据的一行
#布尔型索引可以应用于数据的删选
data[names=='Joe']
array([[-0.11616092,  1.07999647, -0.35885284, -0.84570262]])
#布尔型索引应用修改值
#选取所有Mor的行，并且全部值   赋值为0
data[names=='Mor'] = 0
data
array([[ 0.30878037, -0.4096957 , -0.83750594, -0.97213605],
       [ 0.        ,  0.        ,  0.        ,  0.        ],
       [-1.16628504, -0.4982823 ,  1.53364224, -1.15853535],
       [-0.11616092,  1.07999647, -0.35885284, -0.84570262],
       [ 0.        ,  0.        ,  0.        ,  0.        ],
       [ 1.45718967, -1.14880644,  0.09459774, -0.25857695],
       [-0.2095555 , -0.53830113,  0.63900549,  0.05845763]])
data[names=='Will',2:]=0
data
array([[ 0.30878037, -0.4096957 , -0.83750594, -0.97213605],
       [ 0.        ,  0.        ,  0.        ,  0.        ],
       [-1.16628504, -0.4982823 ,  0.        ,  0.        ],
       [-0.11616092,  1.07999647, -0.35885284, -0.84570262],
       [ 0.        ,  0.        ,  0.        ,  0.        ],
       [ 1.45718967, -1.14880644,  0.        ,  0.        ],
       [-0.2095555 , -0.53830113,  0.        ,  0.        ]])