Matrix (list-in-list), how to get a column?

[F. Petitjean]

On Thu, 21 Oct 2004 17:19:04 +0200, Arvid Andersson <arvid at linux.se> wrote:
> 
> I have some data that looks like this:
> data = [[1, 2], [3, 4], [5, 6]]
> 
> I want to send columns 1 and 2 to a function
> as two variables, say "plot(col1,col2)".
> 
>From a interpreter session :
>>> data = [[1, 2], [3, 4], [5, 6]]
>>> col1 = [ pt[0] for pt in data ]
>>> col1
[1, 3, 5]

>>> import Numeric as N
>>> N.array(data)
array([[1, 2],
       [3, 4],
       [5, 6]])
>>> N.array(data, N.Float)
array([[ 1.,  2.],
       [ 3.,  4.],
       [ 5.,  6.]])

>>> pts = N.array(data, N.Float)
>>> pts[:,0]
array([ 1.,  3.,  5.])

Hope that helps.  Don't hesitate to try directly at the interpreter
prompt.