Problem involving sets...

[flamesrock]

Kind of a fun but confusing problem...

I have two lists. Each list contains elements of two-element lists.
l1 = [['c1',1],['c2',2],['c3',4]]
l2 = [['c1',1],['c2',2],['c4',4],['c3',3]]

Exactly in this format, where
superlist[0][0] is always a string
superlist[0][1] is always an integer

Now what I would like to do is find the intersect of those two
super-lists based on superlist[0][0] and then compare the integers to
find ultimately:
A list of strings of the intersect of l1/l2, where the l1[x][1] >
l2[x][1]
In the case of the above example, that would be simply:
['c3']


But since lists are unhashable, I can't make a set consisting of
lists... Maybe I am making this problem too difficult by thinking in
terms of sets. Does anyone have a simple solution????

-Thanks

[Felipe Almeida Lessa]

Re: Problem involving sets...

Em Sex, 2006-04-14 às 15:43 -0700, flamesrock escreveu:[color=blue]
> Does anyone have a simple solution????[/color]

$ python2.4
Python 2.4.3 (#2, Mar 30 2006, 21:52:26)
[GCC 4.0.3 (Debian 4.0.3-1)] on linux2
Type "help", "copyright" , "credits" or "license" for more information.[color=blue][color=green][color=darkred]
>>> l1 = [['c1',1],['c2',2],['c3',4]]
>>> l2 = [['c1',1],['c2',2],['c4',4],['c3',3]]
>>> print [tuple(x) for x in l1][/color][/color][/color]
[('c1', 1), ('c2', 2), ('c3', 4)][color=blue][color=green][color=darkred]
>>> print [tuple(x) for x in l2][/color][/color][/color]
[('c1', 1), ('c2', 2), ('c4', 4), ('c3', 3)][color=blue][color=green][color=darkred]
>>> s1 = frozenset(tuple (x) for x in l1)
>>> s2 = frozenset(tuple (x) for x in l2)
>>> print s1[/color][/color][/color]
frozenset([('c2', 2), ('c1', 1), ('c3', 4)])[color=blue][color=green][color=darkred]
>>> print s2[/color][/color][/color]
frozenset([('c2', 2), ('c4', 4), ('c3', 3), ('c1', 1)])[color=blue][color=green][color=darkred]
>>> print s2-s1[/color][/color][/color]
frozenset([('c4', 4), ('c3', 3)])[color=blue][color=green][color=darkred]
>>> print[list(x) for x in s2-s1][/color][/color][/color]
[['c4', 4], ['c3', 3]]


--
Felipe.

[Kent Johnson]

Re: Problem involving sets...

flamesrock wrote:[color=blue]
> Kind of a fun but confusing problem...
>
> I have two lists. Each list contains elements of two-element lists.
> l1 = [['c1',1],['c2',2],['c3',4]]
> l2 = [['c1',1],['c2',2],['c4',4],['c3',3]]
>
> Exactly in this format, where
> superlist[0][0] is always a string
> superlist[0][1] is always an integer
>
> Now what I would like to do is find the intersect of those two
> super-lists based on superlist[0][0] and then compare the integers to
> find ultimately:
> A list of strings of the intersect of l1/l2, where the l1[x][1] >
> l2[x][1]
> In the case of the above example, that would be simply:
> ['c3'][/color]

In [5]: l1 = [['c1',1],['c2',2],['c3',4]]

In [6]: l2 = [['c1',1],['c2',2],['c4',4],['c3',3]]

In [7]: d=dict(l1)

In [10]: [k for k,v in l2 if k in d and v < d[k]]
Out[10]: ['c3']

Kent

[flamesrock]

Re: Problem involving sets...

wowowow now THAT is what I call simple!

[Dave Hughes]

Re: Problem involving sets...

Kent Johnson wrote:
[color=blue]
> flamesrock wrote:[color=green]
> > Kind of a fun but confusing problem...
> >
> > I have two lists. Each list contains elements of two-element lists.
> > l1 = [['c1',1],['c2',2],['c3',4]]
> > l2 = [['c1',1],['c2',2],['c4',4],['c3',3]]
> >
> > Exactly in this format, where
> > superlist[0][0] is always a string
> > superlist[0][1] is always an integer
> >
> > Now what I would like to do is find the intersect of those two
> > super-lists based on superlist[0][0] and then compare the integers
> > to find ultimately:
> > A list of strings of the intersect of l1/l2, where the l1[x][1] >
> > l2[x][1]
> > In the case of the above example, that would be simply:
> > ['c3'][/color]
>
> In [5]: l1 = [['c1',1],['c2',2],['c3',4]]
>
> In [6]: l2 = [['c1',1],['c2',2],['c4',4],['c3',3]]
>
> In [7]: d=dict(l1)
>
> In [10]: [k for k,v in l2 if k in d and v < d[k]]
> Out[10]: ['c3']
>
> Kent[/color]

The dict solution posted above is definitely better than the following,
but purely out of idle curiosity I was interested to see if this could
be done in one line using just list comprehensions ...

Python 2.4.2 (#1, Nov 15 2005, 15:54:06)
[GCC 3.3.6 (Gentoo 3.3.6, ssp-3.3.6-1.0, pie-8.7.8)] on linux2
Type "help", "copyright" , "credits" or "license" for more information.[color=blue][color=green][color=darkred]
>>> l1 = [['c1',1],['c2',2],['c3',4]]
>>> l2 = [['c1',1],['c2',2],['c4',4],['c3',3]]
>>> [k2 for [k2,v2] in l2 if k2 in [k1 for k1,v1 in l1] and v2 < [v1[/color][/color][/color]
for k1,v1 in l1 if k1 == k2][0]]
['c3']

.... yup :-)


Dave.
--