How to sort a list? NOT a newbie question.

Tim Roberts timr at probo.com
Wed Sep 19 07:54:06 CEST 2001


mjbarber at ascc.artsci.wustl.edu (Michael James Barber) wrote:

>All in Python 2.1.1:
>
>>>> l1 = [1, '1j', [1,'1j']]
>>>> l1.sort()
>>>> print l1
>[1, [1, '1j'], '1j']
>
>>>> l2 = [1, 1j, [1,'1j']]
>>>> l2.sort()
>Traceback (most recent call last):
>  File "<input>", line 1, in ?
>TypeError: cannot compare complex numbers using <, <=, >, >=
>
>
>This came up in the context of building the coefficients of polynomials 
>from a list of roots.  If complex roots occur in complex conjugate pairs, 
>then the resulting coefficients must be real, so I decided to cast the 
>coefficients to floats in this case.  A straightforward test is to take 
>the complex conjugate of each element of the list, then sort both lists 
>and see if they are the same.  As is clear from the above, that definitely 
>didn't work!  

You can make this work if you can answer a couple of simple questions.  

Which is greater:  3 or 3j?

Put these numbers in order:   3+0j  1+1j  1+2j  2+1j  2+2j   1+0j  0+3j
--
- Tim Roberts, timr at probo.com
  Providenza & Boekelheide, Inc.



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