help with slicing/replacing matrix sections.

[Robert Kern]

Erik Lind wrote:
> I see a more complicated thread on a similar sounding question, but my 
> question is simpler, I hope.

numpy questions are usually answered better on the numpy mailing list.

   http://www.scipy.org/Mailing_Lists

> I have a large numpy matrix, initially created as:
> 
> Mat = zeros((a,b), int)
> 
> and a smaller array with other data
> 
> Sub = [1,2,3,4,5],[6,7,8,9,0]
> 
> I want to replace a section of Mat matrix with Sub matrix without having to 
> loop through each cell in each matrix individually.
> 
> I thought index/slice assignments, should be able to do that, but I can only 
> get it to work (as per book examples) with simple arrays. Every syntax 
> combination I have tried gives one error or another, typically "can't 
> broadcast an object....", but intuitively it seems there should be a simple 
> solution.
> 
> In short, how do I insert the data in the two (or any number of) rows in 
> Sub[0:2] into any part of Mat starting at Mat[x,y] without using "for" loops 
> ? 

In [11]: Sub = array([[1,2,3,4,5],[6,7,8,9,0]])

In [12]: Mat = zeros((10, 10), int)

In [13]: Mat[5:5+2,4:4+5] = Sub

In [14]: Mat
Out[14]:
array([[0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        [0, 0, 0, 0, 1, 2, 3, 4, 5, 0],
        [0, 0, 0, 0, 6, 7, 8, 9, 0, 0],
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]])

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco