how to shrink a numarray array?

[Qiangning Hong]

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...

--
Qiangning Hong

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[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