Inverse of dict(zip(x,y))

psykeedelik icymist at gmail.com
Thu Mar 5 19:07:02 CET 2009


On Mar 5, 6:01 pm, Tino Wildenhain <t... at wildenhain.de> wrote:
> Piet van Oostrum wrote:
> >>>>>> Andre Engels <andreeng... at gmail.com> (AE) wrote:
>
> >> AE> On Wed, Mar 4, 2009 at 11:02 AM, lone_eagle <icym... at gmail.com> wrote:
> >>>> Can someone suggest a easy method to do the inverse of dict(zip(x,y))
> >>>> to get two lists x and y?
>
> >>>> So, if x and y are two lists, it is easier to make a dictionary using
> >>>> d = dict(zip(x,y)), but if I have d of the form, d = {x1:y1,
> >>>> x2:y2, ...}, what is there any trick to get lists x = [x1, x2, ...]
> >>>> and y = [y1, y2, ...]
>
> >> AE> x = d.keys()
> >> AE> y = [d[e] for d in x]
>
> >> AE> y = d.values() might also work, but I am not sure whether d.keys() and
> >> AE> d.values() are guaranteed to use the same order.
>
> > Yes, they are if the dictionary is not changed in the meantime (not even
> > inserting and removing the same thing). See the library documentation,
> > section dict.
>
> Still I'd like to see an application where this really matters (that
> keys() and values() match in order)
>
> Tino
>
>  smime.p7s
> 4KViewDownload

First, thanks to all the guys who posted replies to my query!!

And then, just as an example to what Tino raised ...

I usually get properties that I compute, in a dictionary like property
= [key1: val1, key2:val2, ...] and then I usually want to plot them in
pylab, which AFAIK requires x and y as lists for the plot argument.
Then I need to get the lists [key1, key2, ...] and [val1, val2, ...].
And now I wonder if there a more efficient way doing what I described
above!! ;)

Cheers,
Chaitanya



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