Welcome, William!
You are probably looking for “random()”, which has the same syntax as
“zeroes()” but returns a vector of pseudorandom values on [0,1).
To make a vector of a million of those, use “$a = random(1e6)”.
To make random integers based on a histogram that you already have in-hand, a
simple way is:
$vec = pdl(0,1,1,1,2,2,2,3); # note 8 values
$rand = $vec->(floor(random(1e6) * 8))->sever;
The “random(1e6”) makes a million elements on [0,1). Multiply by 8 and take
the floor to get integers on [0,7]. The outermost operation indexes $vec with
the corresponding random value. Since there are three 1’s, 1 is three times
as likely in the output.
Does that work?
Best,
Craig
> On Apr 6, 2018, at 5:16 PM, William Schmidt <[email protected]>
> wrote:
>
> Hello Piddlers,
>
> I am moving from R to PDL, with tons of experience with Perl, lots with R but
> zero with PDL,
> so this is a pretty basic question. I can see from the PDL Book that PDL is
> very
> sophisticated, with much more functionality than I will ever use, but I want
> to master basic PDL to leverage my Perl. My focus is on probability in two
> dimensions so
> I will be working mostly with 1-dimensional vectors. Here is an example from
> R that
> I would like to learn how to do in PDL. It is a small example but once I
> master
> the construction of this data I will extend it to much larger vectors.
>
> Suppose I have random variable X whose values and probabilities are as
> follows:
>
> x p(x)
> 0 1/8
> 1 3/8
> 2 3/8
> 3 1/8
>
> To get a sample of 50 random values drawn from this population with
> replacement in R I
> would say:
>
> x <- seq.int <http://seq.int/>(0,3) # Concatenate a sequence of ints
> from 0 to 3.
> x # print x.
> [1] 0 1 2 3
>
> weights <- c(1/8, 3/8, 3/8, 1/8) # Another form of concatenation.
> weights
> [1] 0.125 0.375 0.375 0.125
>
> s <- sample(x, 50, replace=TRUE, prob=weights)
> s
> [1] 0 1 1 3 2 2 2 3 2 0 0 1 3 1 1 3 0 2 1 2 2 1 3 1 2 2 0 2 2 2 3 2
> [33] 1 1 3 1 2 2 1 1 0 1 3 2 2 1 3 0 1 1
>
> I can now manipulate s, calculate its statistical properties and graph its
> probability distribution. Fifty integer values is not very interesting but
> the problems I am studying have thousands of values and very different
> weights. How do I do this in PDL? I have PDL::Stats::Basic and
> PDL::Stats::Distr installed along with PGPLOT but it's generating this basic
> data that has me stumped.
>
> Thanks and regards,
>
> Will Schmidt
> [email protected] <mailto:[email protected]>
>
>
>
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