CODEWITHSUNDEEP
pythonalgorithmpython-3.xmatrixmin
S.Troy
S.Troy

Reputation: 117

Minimum value in each row and each column of a matrix - Python

Can someone please help me out? I am trying to get the minimum value of each row and of each column of this matrix 

matrix =[[12,34,28,16],
        [13,32,36,12],
        [15,32,32,14],
        [11,33,36,10]]

So for example: I would want my program to print out that 12 is the minimum value of row 1 and so on.

Upvotes: 2

Views: 6818

Answers (2)

timgeb
timgeb

Reputation: 78690

Use numpy.

>>> import numpy as np
>>> matrix =[[12,34,28,16],
...         [13,32,36,12],
...         [15,32,32,14],
...         [11,33,36,10]]
>>> np.min(matrix, axis=1) # computes minimum in each row 
array([12, 12, 14, 10])
>>> np.min(matrix, axis=0) # computes minimum in each column
array([11, 32, 28, 10])

Upvotes: 3

ForceBru
ForceBru

Reputation: 44838

Let's repeat the task statement: "get the minimum value of each row and of each column of this matrix".

Okay, so, if the matrix has n rows, you should get n minimum values, one for each row. Sounds interesting, doesn't it? So, the code'll look like this:

result1 = [<something> for row in matrix]

Well, what do you need to do with each row? Right, find the minimum value, which is super easy:

result1 = [min(row) for row in matrix]

As a result, you'll get a list of n values, just as expected.

Wait, by now we've only found the minimums for each row, but not for each column, so let's do this as well!

Given that you're using Python 3.x, you can do some pretty amazing stuff. For example, you can loop over columns easily:

result2 = [min(column) for column in zip(*matrix)] # notice the asterisk!

The asterisk in zip(*matrix) makes each row of matrix a separate argument of zip's, like this:

zip(matrix[0], matrix[1], matrix[2], matrix[3])

This doesn't look very readable and is dependent on the number of rows in matrix (basically, you'll have to hard-code them), and the asterisk lets you write much cleaner code.

zip returns tuples, and the ith tuple contains the ith values of all the rows, so these tuples are actually the columns of the given matrix.

Now, you may find this code a bit ugly, you may want to write the same thing in a more concise way. Sure enough, you can use some functional programming magic:

result1 = list(map(min, matrix))
result2 = list(map(min, zip(*matrix)))

These two approaches are absolutely equivalent.

Upvotes: 6

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