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Python3 custom algorithm sorting

Sorted (A1, key = functools.cmp_to_key (cmp))

A1 is to be sorted list,cmp is the sorting function

Numpy

T An is the x parameter matrix, and vstack is to add a column of 1 as the offset term.

[0] An is the parameter matrix and y is the corresponding value of x. The function of the function is to fit k and b by the least square method.

A = [1, 2, 3] b = [4, 5, 5, 6]

A.append (b)

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

A.extend (b)

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

Size usage

Import numpy as np

X=np.array ([1, 2, 3, 4]

[5,6,7,8]

[9, 10, 11, 12]))

Number=X.size # counts all elements in X

X_row=np.size (XPower0) # calculates the number of elements in a row of X

X_col=np.size (XPower1) # calculates the number of elements in a column of X

Print ("number:", number)

Print ("X_row:", X_row)

Print ("X_col:", X_col)

Number: 12

X_row: 3

X_col: 4

The usage of shape

Import numpy as np

X=np.array ([1, 2, 3, 4]

[5,6,7,8]

[9, 10, 11, 12]))

X_dim=X.shape # returns the dimension of the array as a tuple

Print ("X_dim:", X_dim)

Print (X.shape [0]) # number of output lines

Print (X.shape [1]) # number of output columns

X_dim: (3,4)

three

four

The usage of len

Import numpy as np

X=np.array ([1, 2, 3, 4]

[5,6,7,8]

[9, 10, 11, 12]))

Length=len (X) # returns the length of the object is not the number of elements

Print ("length of X:", length)

Length of X: 3

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