關於利用資料集繪圖建立模型

>>> import regression
>>> xArr, yArr= regression.loadDataSet('ex0.txt')
>>> ws= regression.standRegres(xArr,yArr)
>>> xMat =mat(xArr)
>>> yMat = mat(yArr)
>>> yHat = xMat*ws
>>> import matplotlib.pyplot as plt
>>> fig = plt.figure()
>>> ax = fig.add_subplot(111)
>>> ax.scatter(xMat[:,1].flatten().A[0],yMat.T[:,0].flatten().A[0])
<matplotlib.collections.PathCollection object at 0x0000023DD0AEFEF0>
>>> xCopy = xMat.copy()
>>> xCopy.sort(0)
>>> yHat  = xCopy *ws
>>> ax.plot(xCopy[:,1],yHat)
[<matplotlib.lines.Line2D object at 0x0000023DD08DD470>]
>>> plt.show()
 

flatten()函式用法

flatten是numpy.ndarray.flatten的一個函式，即返回一個摺疊成一維的陣列。但是該函式只能適用於numpy物件，即array或者mat，普通的list列表是不行的。 

a是個矩陣或者陣列，a.flatten()就是把a降到一維，預設是按橫的方向降 
那麼a.flatten().A又是什麼呢? 其實這是因為此時的a是個矩陣，降維後還是個矩陣，矩陣.A（等效於矩陣.getA()）變成了陣列。

問題：關於矩陣套矩陣（未解決）

>>> x = matrix([[1,0],[0,0]])
>>> y = matrix([[2,2],[1,1]])
>>> z = y[x]
>>> z
matrix([[[1, 1],
         [2, 2]],

        [[2, 2],
         [2, 2]]])
>>> x = matrix([[1,2],[3,4]])
>>> z
matrix([[[1, 1],
         [2, 2]],

        [[2, 2],
         [2, 2]]])
>>> y = matrix([[2,2],[1,1]])
>>> z
matrix([[[1, 1],
         [2, 2]],

        [[2, 2],
         [2, 2]]])
>>> y = matrix([[1,1],[2,2]])
>>> 
>>> z
matrix([[[1, 1],
         [2, 2]],

        [[2, 2],
         [2, 2]]])
>>> y = matrix([[1,2],[2,1]])
>>> z
matrix([[[1, 1],
         [2, 2]],

        [[2, 2],
         [2, 2]]])
>>> z = x[y]





>>> x = matrix([[1,0],[0,0]])
>>> y = matrix([[2,2],[1,1]])
>>> z = y[x]
>>> z = x[y]
Traceback (most recent call last):
  File "<pyshell#129>", line 1, in <module>
    z = x[y]
  File "C:\Users\34856\AppData\Local\Programs\Python\Python36\lib\site-packages\numpy\matrixlib\defmatrix.py", line 190, in __getitem__
    out = N.ndarray.__getitem__(self, index)
IndexError: index 2 is out of bounds for axis 0 with size 2