generating random tuples in python

Aaron Brady castironpi at gmail.com
Tue Apr 21 09:19:12 CEST 2009


On Apr 20, 11:04 pm, per <perfr... at gmail.com> wrote:
> On Apr 20, 11:08 pm, Steven D'Aprano
>
>
>
> <ste... at REMOVE.THIS.cybersource.com.au> wrote:
> > On Mon, 20 Apr 2009 11:39:35 -0700, per wrote:
> > > hi all,
>
> > > i am generating a list of random tuples of numbers between 0 and 1 using
> > > the rand() function, as follows:
>
> > > for i in range(0, n):
> > >   rand_tuple = (rand(), rand(), rand()) mylist.append(rand_tuple)
>
> > > when i generate this list, some of the random tuples might be very close
> > > to each other, numerically. for example, i might get:
> > [...]
> > > how can i maximize the amount of "numeric distance" between the elements
> > > of
> > > this list, but still make sure that all the tuples have numbers strictly
> > > between 0 and 1 (inclusive)?
>
> > Well, the only way to *maximise* the distance between the elements is to
> > set them to (0.0, 0.5, 1.0).
>
> > > in other words i want the list of random numbers to be arbitrarily
> > > different (which is why i am using rand()) but as different from other
> > > tuples in the list as possible.
>
> > That means that the numbers you are generating will no longer be
> > uniformly distributed, they will be biased. That's okay, but you need to
> > describe *how* you want them biased. What precisely do you mean by
> > "maximizing the distance"?
>
> > For example, here's one strategy: you need three random numbers, so
> > divide the complete range 0-1 into three: generate three random numbers
> > between 0 and 1/3.0, called x, y, z, and return [x, 1/3.0 + y, 2/3.0 + z].
>
> > You might even decide to shuffle the list before returning them.
>
> > But note that you might still happen to get (say) [0.332, 0.334, 0.668]
> > or similar. That's the thing with randomness.
>
> > --
> > Steven
>
> i realize my example in the original post was misleading. i dont want
> to maximize the difference between individual members of a single
> tuple -- i want to maximize the difference between distinct tuples. in
> other words, it's ok to have (.332, .334, .38), as long as the other
> tuple is, say, (.52, .6, .9) which is very difference from (.332, .
> 334, .38).  i want the member of a given tuple to be arbitrary, e.g.
> something like (rand(), rand(), rand()) but that the tuples be very
> different from each other.
>
> to be more formal by very different, i would be happy if they were
> maximally distant in ordinary euclidean space... so if you just plot
> the 3-tuples on x, y, z i want them to all be very different from each
> other.  i realize this is obviously biased and that the tuples are not
> uniformly distributed -- that's exactly what i want...
>
> any ideas on how to go about this?
>
> thank you.

Two ideas.  One, start with a square grid and jitter the individual
points by a small random amount.  Two, start with one point, and move
from it by a random large distance: a2= a1+ .5+ rand( ), then %1.



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