how to shrink a numarray array?

[Diez B. Roggisch]

Qiangning Hong wrote:
> To draw a large array of data on a small panel, I need to shrink it to a
> given size. e.g:
> 
> To draw numarray.arange(10000) on a panel of width of 100, I only need
> to draw the points of (0, 100, 200, 300, ...) instead of (0, 1, 2, ...).
>   So I need a method to shrink it to an 100-item array.
> 
> x[::len(x)/panel_width] will not work. If the panel's width is 60, that
> expression will return an array of 61 elements.
> 
> I believe there is an existing function in numarray to do this, however
> English is not my mother tongue and math is not my speciality, I can't
> find it in the document full of math terms...
> 

You can do that with bresenham's algortithm. But that's been sooo long 
since I did that the last time...  The basic idea is that you us the 
larger of the values (your columncount) as a threshold. The you do 
msomething like this:

columncount = 600
image_width = 60
v = 0
cols_to_pick = [0]
for i in xrange(columncount):
     if v >= columncount:
         v -= columncount
         cols_to_pick.append(i)
     v += image_width



Maybe a better idea is to try and find image scaling algorithms -they 
might even do filtering for you.

Diez