[云炬python3玩转机器学习笔记] 3-5Numpy数组和矩阵的基本操作

import numpy as npx=np.arange(10)xarray([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])X= np.arange(15).reshape(3,5)Xarray([[ 0, 1, 2, 3, 4],[ 5, 6, 7, 8, 9],[10, 11, 12, 13, 14]])基本属性x.ndim # 查看数组维数1X.ndim2x.shape(10,)X.shape(3, 5)x.size10X.size15numpy.array的数据访问xarray([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])x[0]0x[-1]9Xarray([[ 0, 1, 2, 3, 4],[ 5, 6, 7, 8, 9],[10, 11, 12, 13, 14]])X[0][0]0X[(0,0)]0X[2,2]12xarray([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])x[0:5]array([0, 1, 2, 3, 4])x[:5]array([0, 1, 2, 3, 4])x[5:]array([5, 6, 7, 8, 9])x[::2] #间隔array([0, 2, 4, 6, 8])x[::-1] #倒序array([9, 8, 7, 6, 5, 4, 3, 2, 1, 0])Xarray([[ 0, 1, 2, 3, 4],[ 5, 6, 7, 8, 9],[10, 11, 12, 13, 14]])X[:2,:3]array([[0, 1, 2],[5, 6, 7]])X[:2][:3] #前两行的前三列array([[0, 1, 2, 3, 4],[5, 6, 7, 8, 9]])X[:2][:3] #X[:2]的前3行array([[0, 1, 2, 3, 4],[5, 6, 7, 8, 9]])X[:2,::2] array([[0, 2, 4],[5, 7, 9]])X[::-1,::-1]array([[14, 13, 12, 11, 10],[ 9, 8, 7, 6, 5],[ 4, 3, 2, 1, 0]])X[0]array([0, 1, 2, 3, 4])X[0,:]array([0, 1, 2, 3, 4])X[0,:].ndim1X[:,0]array([ 0, 5, 10])X[:,0].ndim1subX=X[:2,:3]subXarray([[0, 1, 2],[5, 6, 7]])subX[0,0]=100subXarray([[100, 1, 2],[ 5, 6, 7]])X #子矩阵对原矩阵右影响，子矩阵引用的原矩阵的元素array([[100, 1, 2, 3, 4],[ 5, 6, 7, 8, 9],[ 10, 11, 12, 13, 14]])X[0,0]=0Xarray([[ 0, 1, 2, 3, 4],[ 5, 6, 7, 8, 9],[10, 11, 12, 13, 14]])subXarray([[0, 1, 2],[5, 6, 7]])subX =X[:2,:3].copy() #副本subXarray([[0, 1, 2],[5, 6, 7]])subX[0,0]=100subXarray([[100, 1, 2],[ 5, 6, 7]])Xarray([[ 0, 1, 2, 3, 4],[ 5, 6, 7, 8, 9],[10, 11, 12, 13, 14]])Reshapex.shape(10,)x.ndim1x.reshape(2,5)array([[0, 1, 2, 3, 4],[5, 6, 7, 8, 9]])xarray([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])A= x.reshape(2,5)Aarray([[0, 1, 2, 3, 4],[5, 6, 7, 8, 9]])xarray([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])B= x.reshape(1,10)B #一维转二维array([[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]])B.shape(1, 10)x.reshape(10,-1) #指定行数，智能计算列数array([[0],[1],[2],[3],[4],[5],[6],[7],[8],[9]])x.reshape(-1,10)array([[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]])x.reshape(2,-1)array([[0, 1, 2, 3, 4],[5, 6, 7, 8, 9]])x.reshape(3,-1)---------------------------------------------------------------------------ValueError Traceback (most recent call last)<ipython-input-65-27fb2acd3ab6> in <module>----> 1 x.reshape(3,-1)ValueError: cannot reshape array of size 10 into shape (3,newaxis)