Hello,
> I was just messing with dictionaries and lists, and I wonder if we
> could solve the problem once and for all with an inefficient generic
> solution. Here's the thing :
>
> I often have to define both a function, and its inverse. Something like :
>
> d = {
> 'a' : 1,
> 'b' : 2,
> 'c' : 1,
> 'd' : 3
> }
>
> Then, I want to find the list of all elements whose image is a 1, or
> 2, or 3, and end up defining the following dictionary :
>
> d_inv = {
> 1 : ['a','c'],
> 2 : ['b'],
> 3 : ['d']
> }
>
> Aaaaaand it would be sooo nice if there was a way to write d**(-1)[2],
> or something of the kind ! Did you ever write a code like this, and
> would you be interested by a generic tool for that ?
>
> Otherwise I'll just keep on computing the inverse of my dictionaries
> with a couple of Python lines ;-)
There is something liek that in finite_set_maps:
sage: sage.sets.finite_set_map_cy.fibers(d.get, d.keys())
{1: {'a', 'c'}, 2: {'b'}, 3: {'d'}}
Any suggestion to put it at a better place is welcome !
Cheers,
Florent
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