Reading text file containing square matrix

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December 3rd, 2012, 05:37 PM

rebork

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Reading text file containing square matrix

Hi everyone,

I am a beginner at python and so far it's been great learning this language. I'm currently working on an assignment which is asking me to do some operations on a multidimensional square matrix. My problem is getting the matrix out of a text file because I just can't figure out how to get it out. I can print the matrix but I can never do anything to it like find its dot product or transpose.

My code so far...

Code:

from numpy import *

textfile=raw_input('What is your textfile name? (Refrain from putting .txt):')
print 'You have entered', textfile+'.txt'
new_copy=[]
filename=open(textfile+'.txt')
for line in filename:
	new_copy.append(line)
print new_copy

Any help would be gladly appreciated!

December 3rd, 2012, 06:39 PM

b49P23TIvg

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Join Date: Aug 2011

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A solution (without matrix product)

Code:

import pprint

textfile=raw_input('What is your textfile name? (Refrain from putting .txt):')
name = textfile + '.txt'
print 'loading',name

with open(name,'r') as inf:
	text_data = inf.readlines()

table = []
for Line in text_data:
    row = []
    for field in Line.strip().split():
        row.append(float(field))          # convert to float
    table.append(row)

print('the table is:')
pprint.pprint(table)

def transpose(A):
    return list(zip(*A))

print('transposed')
pprint.pprint(transpose(table))

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December 3rd, 2012, 06:44 PM

b49P23TIvg

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Join Date: Aug 2011

Posts: 3,372

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Simpler with numpy

Code:

>>> import numpy
>>> numpy.loadtxt('a.txt')
array([[ 1.,  2.],
       [ 3.,  4.]])
>>> A = numpy.loadtxt('a.txt')
>>> A.transpose()
array([[ 1.,  3.],
       [ 2.,  4.]])
>>> A.dot(A)
array([[  7.,  10.],
       [ 15.,  22.]])
>>>

December 4th, 2012, 12:41 AM

rebork

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Join Date: Dec 2012

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Quote:

Originally Posted by b49P23TIvg

A solution (without matrix product)

Code:

import pprint

textfile=raw_input('What is your textfile name? (Refrain from putting .txt):')
name = textfile + '.txt'
print 'loading',name

with open(name,'r') as inf:
	text_data = inf.readlines()

table = []
for Line in text_data:
    row = []
    for field in Line.strip().split():
        row.append(float(field))          # convert to float
    table.append(row)

print('the table is:')
pprint.pprint(table)

def transpose(A):
    return list(zip(*A))

print('transposed')
pprint.pprint(transpose(table))

Hi I looked through this code and I tried it out using PyLab. Everything worked up till I got the value error stating that I could not convert the string to float at row.append(float(field)). I tried the numpy way too but that also had the problem of converting string to float. Am I doing something wrong?

December 4th, 2012, 07:42 AM

b49P23TIvg

Contributing User

Join Date: Aug 2011

Posts: 3,372

Time spent in forums: 1 Month 2 Weeks 3 Days 11 h 39 m 38 sec
Reputation Power: 383

Yes, you did something wrong. Specifically you didn't share your input file. My test data:

Code:

1 2
3 4

December 4th, 2012, 01:42 PM

rebork

Registered User

Join Date: Dec 2012

Posts: 3

Time spent in forums: 27 m 43 sec
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Ohhh I see. My text file was wrong the enter time! My file contained [[1,1],[2,3]]. But now that I think about it my program probably didn't need the matrix to be displayed as such in a text file. My apologies. Thanks for all your help though I understand it now!

Reading text file containing square matrix

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