indexing lists/arrays question

[a]

On 13 May, 17:41, Carey Tilden <carey.til... at gmail.com> wrote:
> On Thu, May 13, 2010 at 8:45 AM, a <oxfordenergyservi... at googlemail.com> wrote:
> > On 13 May, 16:19, Tim Chase <python.l... at tim.thechases.com> wrote:
> >> On 05/13/2010 09:36 AM, a wrote:
>
> >> > this must be easy but its taken me a couple of hours already
>
> >> > i have
>
> >> > a=[2,3,3,4,5,6]
>
> >> > i want to know the indices where a==3 (ie 1 and 2)
>
> >> indexes = [i for (i, v) in enumerate(a) where v==3]
>
> >> > then i want to reference these in a
>
> >> In a _what_?  You can then do things like
>
> >>    for i in indexes:
> >>      print a[i]
>
> >> (but you already know these are "3", so it's not very exciting...)
>
> >> -tkc
>
> > really its to get the indexes in 1 array where something equals
> > something then reference these in another array.
> > --
> >http://mail.python.org/mailman/listinfo/python-list
>
> Out of curiosity, why are you using two arrays?  Have you considered a
> dict?  There are of course good reasons not to use a dict in this
> situation, but you haven't said one way or another.
>
> Carey

i am reading a 2,n array from one website, column1=times,
column2=values
then another 2,n array from another website, column1=times,
column2=values

the times are different but may (or may not) coincide in places

i need to make a 3rd array, 2,n where the first column are column2
values from array1 and the second column are column2 values from array
2 #where the timestamps agree#

i'm an idl programmer and doing this would be second nature but i need
to make an application which does something along the lines of the
above then plots column2 vs column2 for the above array3 (plus some
other maths).  needs to be non-proprietary and work on different
platforms.  i just started with python, not even sure if it's the best
thing.  the plotting routines seem not to come wrapped with standard
python which is a bit of a pain.

the routine i use most in idl is 'where' and though i managed to write
a def which worked, i couldn't then dereference the list of those
indexes.  i'm a bit old to be learning new languages

thanks for your help!