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[poll] anyone else needs fast random element access off a dictionary?

Peter Hansen peter at engcorp.com
Tue Feb 11 12:28:49 EST 2003 
Michal Vitecek wrote:
> 
>  for example i'm in need of a _fast_ random element access because i use
>  dictionary a) as a mains to have distinct data and b) use the distinct
>  data to make a more diversive population in my memetic algorithm (the
>  more diversive the population is, the better behaviour of the
>  algorithm).
> 
>  currently one can get a random key stored in a dictionary object like
>  this:
> 
>     random.choice(dict.keys())
> 
>  the same goes for a random value stored in a dictionary:
> 
>     random.choice(dict.values())
> 
>  both those methods have one big drawback - they create a list of either
>  keys or values each time a random element is needed which means a very
>  noticeable slowdown. [as a sidenote, random.choice() doesn't work with
>  dictionaries.]

What is wrong with subclassing to create your own object, with
the property of maintaining a list of the keys, or values, or both,
and even a getRandomItem() method which does the above in a very
speedy manner?

That's what object-oriented programming is all about... in this
case it lets you optimize for the frequent case, even though it
might slow down other situations in a fairly minor way.

-Peter
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