单维数组

 # data1 = [6, 7, 8, 9, 10, 1, 2]

 # arr1 =np.array(data1)

 # print(arr1)
>>>>
[ 6  7  8  9 10  1  2]

data2 =[[1,2,3,4],[5,6,7,8]]

arr2 =np.array(data2)

l =arr2.shape   #返回维度

print(arr2)

print(l)
>>>>>

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

data3 =np.arange(1,15)
print(data3)
>>>>>

[ 1  2  3  4  5  6  7  8  9 10 11 12 13 14]

data4 =np.eye(3,3)

print(data4)

>>>

[[1. 0. 0.]
[0. 1. 0.]
[0. 0. 1.]]

* 乘法

lis =[[1,2,3],[4,5,6]]

data1 =np.array(lis)

print(data1)

#矢量化运算可以直接参与运算

l2 =data1*data1

print(l2)

-减法

l3 =data1+data1
print(l3)

>>>>>

[[1 2 3]
[4 5 6]]
[[ 1 4 9]
[16 25 36]]
[[ 2 4 6]
[ 8 10 12]]

l4 =1/data1

print(l4)

>>>>

[[1. 0.5 0.33333333]
[0.25 0.2 0.16666667]]

data2 =np.array([[3,2,1],[6,5,4]])

l4 =data1>data2

print(l4)

>>>>

[[False False  True]

 [False False  True]]

print(arr1[1])

print(arr1[4])

print(arr1[:4])

arr1[1]=888    #给对应索引位置换值

print(arr1)

arr1[:] =55    # 给所有索引位置换值

print(arr1)

>>>>>

2

5

[1 2 3 4]

[  1 888   3   4   5]

[55 55 55 55 55]

arr2d =np.array([[1,2,3],[4,5,6],[7,8,9],[10,11,12]])

print(arr2d)

print(arr2d[3])  #多维数组索引是一维数组

print(arr2d[1][2])    #一维数组以后切牌获得单个值

arr2d[0]=42        #多维数组单独索引赋值,则整个一维数组都换值

arr2d[0][0] =55

print(arr2d)              # 把多为数组都拆开单独赋值获得内容

l =arr2d[0:2]       #多维数组切片,可以

l =arr2d[:2,2]         #切完之后再,进行小切

l =arr2d[:2,1:]       #获取前二行后两列

l =arr2d[2,:2]

l1 =arr2d[1,:2]       #获取第二个前两列

l =arr2d[:3,:2]       #获取前三行前两列

l =arr2d[:,:1]         #多维数组,索引从1开始

print(l)
>>>

[[ 1 2 3]
[ 4 5 6]
[ 7 8 9]
[10 11 12]]
[10 11 12]
6
[[55 42 42]
[ 4 5 6]
[ 7 8 9]
[10 11 12]]
[[55]
[ 4]
[ 7]
[10]]

names =np.array(['bob','bob','bob','bob','bob','apple','alan','sele'])

data =np.random.randn(8,4)

# names =='bob'

print(names=='bob')   #字符串也可以进行比较返回一个bool值

print(names)
>>>>

[ True True True True True False False False]
['bob' 'bob' 'bob' 'bob' 'bob' 'apple' 'alan' 'sele']

print(data)
print(data[names =='bob'])       #有两个bob 所以返回行 #布尔型索数组长度,需要等于布尔型索引长度,
>>>>>

[[-0.3316016 1.78918492 -1.59222587 0.21469427]
[ 1.55247352 1.14508726 -0.68673629 -0.42648069]
[-0.95385141 -0.1938747 0.22302977 -1.25419395]
[ 0.09290589 0.26875941 -0.34120567 1.67205517]
[ 1.17781667 -0.83402007 -2.64528669 -0.70822941]
[ 0.34199013 1.81982055 0.60103061 0.39070584]
[-1.20352138 0.7618197 -1.29754963 1.19821404]
[ 0.84278983 -0.60723742 -0.73442051 -0.87391669]]
[[-0.3316016 1.78918492 -1.59222587 0.21469427]
[ 1.55247352 1.14508726 -0.68673629 -0.42648069]
[-0.95385141 -0.1938747 0.22302977 -1.25419395]
[ 0.09290589 0.26875941 -0.34120567 1.67205517]
[ 1.17781667 -0.83402007 -2.64528669 -0.70822941]]

print(data[names =='bob',2:])         #获取之后也可以切片
print(names!='bob')
print(data[~(names =='bob')])  
>>>>>>>>>>

[[-1.05528931 -0.19176188]
[-1.55590721 0.43000376]
[ 1.3635074 0.75722279]
[ 2.80719722 0.3907232 ]
[ 0.3805182 -1.30951587]]
[False False False False False True True True]
[[ 0.64999255 -1.40220795 -0.11081563 0.51079912]
[ 1.24400895 -1.81700713 -0.24652383 1.20494275]
[-1.53308854 1.09828319 1.32899806 -0.86707369]]