From: a on 13 May 2010 11:15 On 13 May, 15:47, Stefan Behnel <stefan...(a)behnel.de> wrote: > a, 13.05.2010 16:36: > > > 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) > > indices = [ i for i,item in enumerate(a) if item == 3 ] > > > then i want to reference these in a > > print [ a[i] for i in indices ] > > Stefan thanks Stefan. very useful. I didn't get this from the python documentation!
From: Tim Chase on 13 May 2010 11:19 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
From: a on 13 May 2010 11:45 On 13 May, 16:19, Tim Chase <python.l...(a)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.
From: Carey Tilden on 13 May 2010 12:41 On Thu, May 13, 2010 at 8:45 AM, a <oxfordenergyservices(a)googlemail.com> wrote: > On 13 May, 16:19, Tim Chase <python.l...(a)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/pythonlist > 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
From: Tim Chase on 13 May 2010 13:18 On 05/13/2010 10:45 AM, a wrote: >>> 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. If your two arrays are of the same length, you can do things like a = [2,3,3,4,5,6] b = ['a', 'b', 'c', 'd', 'e', 'f'] print [m for (n,m) in zip(a,b) if n == 3] and skip the indexes altogether. tkc
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