Hello,

I want to fill an array with random numbers without resorting to loops, i.e. by doing something like the following, if it were possible:

  fill!(function double(){ return uniform(0.0, 1.0);})(x[]);

Is there a simple way of doing this?

Thank you,
Dominic Jones

P.S. I am aware of the function uniformDistribution, but it makes the sum of the elements equal to 1, which I don't want.

dominic jones:

> I want to fill an array with random numbers without resorting to loops, i.e. by doing something like the following, if it were possible:
>
>   fill!(function double(){ return uniform(0.0, 1.0);})(x[]);
>
> Is there a simple way of doing this?

Generally it's a good idea to use only pure functions inside the higher order functions of Phobos. using impure functions like uniforms could lead to bugs or performance problems.

This is a way to do it (untested):

x.copy(x.length.iota.map!(_ => uniform(0.0, 1.0));

Bye,
bearophile

On 2013-10-10, 16:04, bearophile wrote:

> dominic jones:
>
>> I want to fill an array with random numbers without resorting to loops, i.e. by doing something like the following, if it were possible:
>>
>>   fill!(function double(){ return uniform(0.0, 1.0);})(x[]);
>>
>> Is there a simple way of doing this?
>
> Generally it's a good idea to use only pure functions inside the higher order functions of Phobos. using impure functions like uniforms could lead to bugs or performance problems.
>
> This is a way to do it (untested):
>
> x.copy(x.length.iota.map!(_ => uniform(0.0, 1.0));

You've got the order wrong - copy takes first the source, then the target.
Also, is it faster to use .length.iota than simply mapping on x?
My solution:

x.map!(_=>uniform(0.0, 1.0)).copy(x);

-- 
Simen

Simen Kjaeraas:

> You've got the order wrong - copy takes first the source, then the target.

I'd like it to be (re)named "copyTo" to avoid me such common mistake.

Bye,
bearophile