How can I represent matrices in python?
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4 Answers
Take a look at this answer:
from numpy import matrix
from numpy import linalg
A = matrix( [[1,2,3],[11,12,13],[21,22,23]]) # Creates a matrix.
x = matrix( [[1],[2],[3]] ) # Creates a matrix (like a column vector).
y = matrix( [[1,2,3]] ) # Creates a matrix (like a row vector).
print A.T # Transpose of A.
print A*x # Matrix multiplication of A and x.
print A.I # Inverse of A.
print linalg.solve(A, x) # Solve the linear equation system.
2 Comments
jasonleonhard
Glad you cited the source. Not thrilled you copied the answer from someone else and did not provide you own explanation. Hard to believe this is currently the accepted answer and highest voted. Perhaps you could put a little effort in to explain "your answer"?
Jules Gagnon-Marchand
Most of the time in machine learning, people don't use the NumPy matrix class, but instead create NumPy
ndarray objects with one of the following helper functions: np.empty, np.random.rand, np.ones, etc.Python doesn't have matrices. You can use a list of lists or NumPy
Comments
If you are not going to use the NumPy library, you can use the nested list. This is code to implement the dynamic nested list (2-dimensional lists).
Let r is the number of rows
let r=3
m=[]
for i in range(r):
m.append([int(x) for x in raw_input().split()])
Any time you can append a row using
m.append([int(x) for x in raw_input().split()])
Above, you have to enter the matrix row-wise. To insert a column:
for i in m:
i.append(x) # x is the value to be added in column
To print the matrix:
print m # all in single row
for i in m:
print i # each row in a different line
Comments
((1,2,3,4),
(5,6,7,8),
(9,0,1,2))
Using tuples instead of lists makes it marginally harder to change the data structure in unwanted ways.
If you are going to do extensive use of those, you are best off wrapping a true number array in a class, so you can define methods and properties on them. (Or, you could NumPy, SciPy, ... if you are going to do your processing with those libraries.)