Re: [Tutor] Problem understanding the asarray function of numpy

2014-09-11 Thread Emile van Sebille 

On 9/11/2014 6:34 AM, Radhika Gaonkar wrote:

I have an implementation of lsa, that I need to modify. I am having some
trouble understanding the code. This is the line where I am stuck:

DocsPerWord = sum(asarray(self.A > 0, 'i'), axis=1)


Python doesn't provide an axis parameter for the sum builtin -- this sum 
function comes from numpy.  See 
http://docs.scipy.org/doc/numpy/reference/generated/numpy.sum.html for 
details.


Emile

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Re: [Tutor] Problem understanding the asarray function of numpy

2014-09-11 Thread Peter Otten 
Radhika Gaonkar wrote:

> I have an implementation of lsa, that I need to modify. I am having some
> trouble understanding the code. This is the line where I am stuck:
> 
> DocsPerWord = sum(asarray(self.A > 0, 'i'), axis=1)
> 
> The link for this implementation is :
> http://www.puffinwarellc.com/index.php/news-and-articles/articles/33-latent-semantic-analysis-tutorial.html?showall=1
> 
> Here, A is a matrix of size vocabulary_Size X number_ofDocs
> As far as the documentation of asarray is concerned, this should return an
> array interpretation of the matrix A. But, we need to sum each row. What
> is happening here?

A numpy array can be multidimensional:

>>> import numpy
>>> a = numpy.asarray([[1,2,3],[4,5,6],[7,8,9]])
>>> a
array([[1, 2, 3],
   [4, 5, 6],
   [7, 8, 9]])
>>> a.shape
(3, 3)
>>> a[0,0]
1
>>> a[2,2]
9

So this "array" works very much like a 3x3 matrix. Now let's investigate 
numpy.sum() (which must not be confused with the Python's built-in sum() 
function):

>>> numpy.sum(a)
45
>>> numpy.sum(a, axis=0)
array([12, 15, 18])
>>> numpy.sum(a, axis=1)
array([ 6, 15, 24])

Playing around in interactive interpreter is often helpful to learn what a 
function or snippet of code does.


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[Tutor] Problem understanding the asarray function of numpy

2014-09-11 Thread Radhika Gaonkar 
I have an implementation of lsa, that I need to modify. I am having some
trouble understanding the code. This is the line where I am stuck:

DocsPerWord = sum(asarray(self.A > 0, 'i'), axis=1)

The link for this implementation is :
http://www.puffinwarellc.com/index.php/news-and-articles/articles/33-latent-semantic-analysis-tutorial.html?showall=1

Here, A is a matrix of size vocabulary_Size X number_ofDocs
As far as the documentation of asarray is concerned, this should return an
array interpretation of the matrix A. But, we need to sum each row. What is
happening here?

Thanks!
--
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