Hi,

I'd like to sample with replacement. But found no simple way.
In particular I want to generate a random string of given letters, say
std.ascii.letters.

Anybody a simpler version than

auto randomString = repeat('a').take(10).map!(c => randomSample(letters, 1, letters.length))().joiner();

?

Jens

On 02/22/2013 04:23 PM, Jens Mueller wrote:
> Hi,
>
> I'd like to sample with replacement. But found no simple way.
> In particular I want to generate a random string of given letters, say
> std.ascii.letters.
>
> Anybody a simpler version than
>
> auto randomString = repeat('a').take(10).map!(c =>  randomSample(letters, 1, letters.length))().joiner();
>
> ?
>
> Jens

Here is another way:

import std.stdio;
import std.algorithm;
import std.ascii;
import std.random;
import std.range;

auto pickOne(R)(R range)
    // insert template constraints here ... :)
{
    return range[uniform(0, range.length)];
}

void main()
{
    writeln(iota(10).map!((_) => pickOne(letters)));
}

Ali

Ali Çehreli:

> auto pickOne(R)(R range)
>     // insert template constraints here ... :)
> {
>     return range[uniform(0, range.length)];
> }

That's the function choice() I'd like in Phobos:
http://d.puremagic.com/issues/show_bug.cgi?id=4851

Note that:
range[uniform(0, range.length)];

is written more compactly as:
range[uniform(0, $)];



> void main()
> {
>     writeln(iota(10).map!((_) => pickOne(letters)));
> }

Instead of "(_)" I think it's better to use a simpler "_".

That's another commonly useful function, often named table(), similar to map() but doesn't pass an index to the callable:

http://reference.wolfram.com/mathematica/ref/Table.html

So it becomes something like:

10.table!({ return letters.choice; }).writeln;

Bye,
bearophile

On 02/22/2013 05:07 PM, bearophile wrote:
> Ali Çehreli:
>
>> auto pickOne(R)(R range)
>> // insert template constraints here ... :)
>> {
>> return range[uniform(0, range.length)];
>> }
>
> That's the function choice() I'd like in Phobos:
> http://d.puremagic.com/issues/show_bug.cgi?id=4851

Agreed.

> Note that:
> range[uniform(0, range.length)];
>
> is written more compactly as:
> range[uniform(0, $)];

Good point. I would think that $ must be "out in the open" to work that way.

>> void main()
>> {
>> writeln(iota(10).map!((_) => pickOne(letters)));
>> }
>
> Instead of "(_)" I think it's better to use a simpler "_".

Mine evolved from the earlier buggy ()=> then I inserted an underscore without realizing to remove the parentheses.

> That's another commonly useful function, often named table(), similar to
> map() but doesn't pass an index to the callable:
>
> http://reference.wolfram.com/mathematica/ref/Table.html

I did need such a function in the past. I have been thinking about the name 'generate' but if 'table' is common already, why not. :)

> So it becomes something like:
>
> 10.table!({ return letters.choice; }).writeln;
>
> Bye,
> bearophile

Ali

On 2/22/13 10:07 PM, bearophile wrote:

> That's another commonly useful function, often named table(), similar to
> map() but doesn't pass an index to the callable:
>
> http://reference.wolfram.com/mathematica/ref/Table.html
>
> So it becomes something like:
>
> 10.table!({ return letters.choice; }).writeln;

Couldn't map! be used with a delegate that doesn't receive any arguments?

Ary Borenszweig:

>> 10.table!({ return letters.choice; }).writeln;
>
> Couldn't map! be used with a delegate that doesn't receive any arguments?

I think map() requires a callable that receives one argument.

table() doesn't need the iota() as map(), it accepts one or more numerical arguments, so it's able to generate 2D arrays, 3D arrays, etc.:

table!(() => letters.choice)(3, 4, 5).writeln;

Bye,
bearophile

Ali Çehreli wrote:
> On 02/22/2013 04:23 PM, Jens Mueller wrote:
> >Hi,
> >
> >I'd like to sample with replacement. But found no simple way.
> >In particular I want to generate a random string of given letters, say
> >std.ascii.letters.
> >
> >Anybody a simpler version than
> >
> >auto randomString = repeat('a').take(10).map!(c =>  randomSample(letters, 1, letters.length))().joiner();
> >
> >?
> >
> >Jens
> 
> Here is another way:
> 
> import std.stdio;
> import std.algorithm;
> import std.ascii;
> import std.random;
> import std.range;
> 
> auto pickOne(R)(R range)
>     // insert template constraints here ... :)
> {
>     return range[uniform(0, range.length)];
> }
> 
> void main()
> {
>     writeln(iota(10).map!((_) => pickOne(letters)));
> }

Thanks that looks better.
Phobos misses a pickOne function.

Jens

bearophile wrote:
> Ary Borenszweig:
> 
> >>10.table!({ return letters.choice; }).writeln;
> >
> >Couldn't map! be used with a delegate that doesn't receive any arguments?
> 
> I think map() requires a callable that receives one argument.
> 
> table() doesn't need the iota() as map(), it accepts one or more
> numerical arguments, so it's able to generate 2D arrays, 3D arrays,
> etc.:
> 
> table!(() => letters.choice)(3, 4, 5).writeln;

This looks almost like a Cartesian product but only specifying the
sizes.
I assume you have an enhancement request? Couldn't find it.

Jens

Jens Mueller:

>> table!(() => letters.choice)(3, 4, 5).writeln;
>
> This looks almost like a Cartesian product but only specifying the sizes.

table() also takes a function, so it's closer to a map() or to minimallyInitializedArray() than to a Cartesian product :-)


> I assume you have an enhancement request? Couldn't find it.

I think I don't have an enhancement request on table().

Bye,
bearophile

Ali Çehreli wrote:
> On 02/22/2013 04:23 PM, Jens Mueller wrote:
> >Hi,
> >
> >I'd like to sample with replacement. But found no simple way.
> >In particular I want to generate a random string of given letters, say
> >std.ascii.letters.
> >
> >Anybody a simpler version than
> >
> >auto randomString = repeat('a').take(10).map!(c =>  randomSample(letters, 1, letters.length))().joiner();
> >
> >?
> >
> >Jens
> 
> Here is another way:
> 
> import std.stdio;
> import std.algorithm;
> import std.ascii;
> import std.random;
> import std.range;
> 
> auto pickOne(R)(R range)
>     // insert template constraints here ... :)
> {
>     return range[uniform(0, range.length)];
> }
> 
> void main()
> {
>     writeln(iota(10).map!((_) => pickOne(letters)));
> }

I think this version also looks good:
void main()
{
	auto randomLetter = () => randomSample(letters, 1, letters.length).front;
	writeln(iota(10).map!(_ => randomLetter()));
}

Which makes me think Phobos is convenient enough in this use case. Just finding a simple way to use it can be a burden. It should be improved with better documentation.

Jens