numpy 入门
基础学习
>>> from numpy import *
>>> eye(4)
array([[1., 0., 0., 0.],
[0., 1., 0., 0.],
[0., 0., 1., 0.],
[0., 0., 0., 1.]])
>>> a = array([1,2,3])
>>> a
array([1, 2, 3])
>>> b=array([[1, 2], [3, 4]])
>>> b
array([[1, 2],
[3, 4]])
>>> c=array([1, 2, 3, 4, 5], ndmin = 2)
>>> c
array([[1, 2, 3, 4, 5]])
>>> d = array([1, 2, 3], dtype = complex)
>>> d
array([1.+0.j, 2.+0.j, 3.+0.j])
>>> dt = dtype('i4')
>>> dt
dtype('int32')
>>> dt = dtype([('age',int8)])
>>> array([(10,),(20,),(30,)], dtype = dt)
array([(10,), (20,), (30,)], dtype=[('age', 'i1')])
>>> a=arange(24)
>>> a
array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23])
>>> a.ndim
1
>>> a.shape
(24,)
>>> a.size
24
>>> a.dtype
dtype('int32')
>>> a.real
array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23])
>>> a.imag
array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0])
>>> a.reshape(2,4,3)
array([[[ 0, 1, 2],
[ 3, 4, 5],
[ 6, 7, 8],
[ 9, 10, 11]],
[[12, 13, 14],
[15, 16, 17],
[18, 19, 20],
[21, 22, 23]]])
>>> zeros((5,), dtype = int)
array([0, 0, 0, 0, 0])
>>> ones([2,2], dtype = int)
array([[1, 1],
[1, 1]])
>>> asarray([1,2,3], dtype = float)
array([1., 2., 3.])
>>> arange(10,20,2,dtype=int)
array([10, 12, 14, 16, 18])
>>> linspace(1,10,5,endpoint=True,retstep=False,dtype=int)
array([ 1, 3, 5, 7, 10])
>>> linspace(1,10,5,endpoint=False,retstep=True,dtype=int)
(array([1, 2, 4, 6, 8]), 1.8)
>>> a = arange(10)
>>> s=slice(2,7,2)
>>> a[s]
array([2, 4, 6])
>>> a[2:7:2]
array([2, 4, 6])
>>> a[2:5]
array([2, 3, 4])
>>> a = array([[1,2,3],[3,4,5],[4,5,6]])
>>> a[...,[0,1]]
array([[1, 2],
[3, 4],
[4, 5]])
>>> a[1,...]
array([3, 4, 5])
>>> a[[0,1],...]
array([[1, 2, 3],
[3, 4, 5]])
>>> x = array([[ 0, 1, 2],[ 3, 4, 5],[ 6, 7, 8],[ 9, 10, 11]])
>>> x[x>5]
array([ 6, 7, 8, 9, 10, 11])
>>> a = array([nan, 1,2,nan,3,4,5])
>>> a[~isnan(a)]
array([1., 2., 3., 4., 5.])
>>> a=array([1,2,3,4])
>>> b=array([10,20,30,40])
>>> c=a*b
>>> c
array([ 10, 40, 90, 160])
>>> a = array([[ 0, 0, 0],
[10,10,10],
[20,20,20],
[30,30,30]])
>>> b=array([1,2,3])
>>> a+b
array([[ 1, 2, 3],
[11, 12, 13],
[21, 22, 23],
[31, 32, 33]])
>>> bb = tile(b, (4, 1))
>>> bb
array([[1, 2, 3],
[1, 2, 3],
[1, 2, 3],
[1, 2, 3]])
>>> for x in nditer(a,op_flags=['readwrite']):
print(x)
0
0
0
10
10
10
20
20
20
30
30
30
>>> for element in a.flat:
print (element)
>>> a.flatten(order='C')
array([ 0, 0, 0, 10, 10, 10, 20, 20, 20, 30, 30, 30])
>>> a.T
array([[ 0, 10, 20, 30],
[ 0, 10, 20, 30],
[ 0, 10, 20, 30]])
>>> b=where(a==20)
>>> b
(array([2, 2, 2], dtype=int64), array([0, 1, 2], dtype=int64))
>>> for i in range(len(b[0])):
print(a[b[0][i]][b[1][i]])
20
20
20
>>> a = array([[1,2],[3,4]])
>>> b=array([[5,6],[7,8]])
>>> concatenate((a,b))
array([[1, 2],
[3, 4],
[5, 6],
[7, 8]])
>>> concatenate((a,b),axis=1)
array([[1, 2, 5, 6],
[3, 4, 7, 8]])
>>> a=[[1,2,3]]
>>> append(a, [[7,8,9]],axis = 0)
array([[1, 2, 3],
[7, 8, 9]])
>>> append(a, [[7,8,9]],axis = 1)
array([[1, 2, 3, 7, 8, 9]])
>>> a=[[1,2,3],[3,4,5]]
>>> np.unique(a)
array([1, 2, 3, 4, 5])
>>> a=array([0,30,45,60,90])
>>> sin(a*pi/180)
array([0. , 0.5 , 0.70710678, 0.8660254 , 1. ])
>>> arcsin(sin(a*pi/180))
array([0. , 0.52359878, 0.78539816, 1.04719755, 1.57079633])
>>> degrees(arcsin(sin(a*pi/180)))
array([ 0., 30., 45., 60., 90.])
>>> around(a, decimals = 1)
array([ 1. , 5.6, 123. , 0.6, 25.5])
>>> around(a, decimals = -1)
array([ 0., 10., 120., 0., 30.])
>>> floor(a)
array([ 1., 5., 123., 0., 25.])
>>> ceil(a)
array([ 1., 6., 123., 1., 26.])
>>> a=array([1,2,3])
>>> b=array([4,5,6])
>>> add(a,b)
array([5, 7, 9])
>>> a+b
array([5, 7, 9])
>>> subtract(a,b)
array([-3, -3, -3])
>>> a-b
array([-3, -3, -3])
>>> multiply(a,b)
array([ 4, 10, 18])
>>> a*b
array([ 4, 10, 18])
>>> divide(a,b)
array([0.25, 0.4 , 0.5 ])
>>> a/b
array([0.25, 0.4 , 0.5 ])
>>> a=array([0.25,1.33,1,100])
>>> a.dtype
dtype('float64')
>>> reciprocal(a)
array([4. , 0.7518797, 1. , 0.01 ])
>>> power(a,2)
array([6.2500e-02, 1.7689e+00, 1.0000e+00, 1.0000e+04])
>>> mod(a,2)
array([0.25, 1.33, 1. , 0. ])
>>> a=array([[3,7,5],[8,4,3],[2,4,9]])
>>> amin(a,1)
array([3, 3, 2])
>>> amin(a,0)
array([2, 4, 3])
>>> amax(a,1)
array([7, 8, 9])
>>> amax(a,0)
array([8, 7, 9])
>>> ptp(a,0)
array([6, 3, 6])
>>> percentile(a, 50)
4.0
>>> median(a)
4.0
>>> mean(a)
5.0
>>> mean(a,0)
array([4.33333333, 5. , 5.66666667])
>>> average([1,2,3, 4],weights = [4,3,2,1], returned = True)
(2.0, 10.0)
>>> std(a)
2.309401076758503
>>> std(a,0)
array([2.62466929, 1.41421356, 2.49443826])
>>> var(a)
5.333333333333333
>>> a
array([[3, 7, 5],
[8, 4, 3],
[2, 4, 9]])
>>> nonzero (a)
(array([0, 0, 0, 1, 1, 1, 2, 2, 2], dtype=int64), array([0, 1, 2, 0, 1, 2, 0, 1, 2], dtype=int64))
>>> condition = mod(a,2) == 0
>>> extract(condition, a)
array([8, 4, 2, 4])
>>> ccc=a.copy()
>>> ccc
array([[3, 7, 5],
[8, 4, 3],
[2, 4, 9]])
np.savetxt("out.txt",a,fmt="%d",delimiter=",")
b = np.loadtxt("out.txt",delimiter=",")