Hello,
I have code which generates a histogram from an array and prints
out the histogram bins/counts. However I cannot get the code to
iterate and print
out the histogram to work.  The following is a minimal example:

import std.range;
import std.stdio;

void main()
{
   ubyte[] data =
[17,32,32,32,38,39,39,47,47,47,47,109,111,111,128];
   uint[ubyte.max - ubyte.min] bins;

   foreach(ubyte val; data) bins[val]++;

   foreach( idx, count; lockstep( iota!ubyte(ubyte.min,
ubyte.max), bins ) )
   {
     if(count > 0 ) {
	writeln("Bin = ", idx, " count = ", count );
     }
   }
}

Alternately:  http://dpaste.com/hold/1267929/

I get the following error messages which I cannot decipher.

test.d(11): Error: template std.range.lockstep does not match any
function template declaration. Candidates are:
/usr/include/dmd/phobos/std/range.d(4724):
std.range.lockstep(Ranges...)(Ranges ranges) if
(allSatisfy!(isInputRange, Ranges))
/usr/include/dmd/phobos/std/range.d(4730):
std.range.lockstep(Ranges...)(Ranges ranges, StoppingPolicy s) if
(allSatisfy!(isInputRange, Ranges))
/usr/include/dmd/phobos/std/range.d(4724): Error: template
std.range.lockstep cannot deduce template function from argument
types !()(Result, uint[255LU])
Failed: 'dmd' '-v' '-o-' 'test.d' '-I.'

Can anyone identify what I am doing wrong.  Also I am curious to
know why std.range includes both Lockstep and lockstep - they
seem like the same thing.

Craig

On 06/24/2013 03:05 PM, Craig Dillabaugh wrote:
> Can anyone identify what I am doing wrong.  Also I am curious to know why std.range includes both Lockstep and lockstep - they seem like the same thing.

lockstep is a helper function that returns an instance of Lockstep.

The reason is that if you instantiate a struct/class template directly you have to explicitly state the template parameters.  A function template call can infer the template parameters and use them to instantiate a class instance.

lockstep(iota!ubyte(ubyte.min, ubyte.max), bins[])

Works, but this leaves you with other errors, I couldn't find a solution
for. Something seems to be wrong with opApply of lockstep.
Or maybe I miss something obvious...

On Monday, 24 June 2013 at 14:15:55 UTC, Joseph Rushton Wakeling
wrote:
> On 06/24/2013 03:05 PM, Craig Dillabaugh wrote:
>> Can anyone identify what I am doing wrong.  Also I am curious to
>> know why std.range includes both Lockstep and lockstep - they
>> seem like the same thing.
>
> lockstep is a helper function that returns an instance of Lockstep.
>
> The reason is that if you instantiate a struct/class template directly you have
> to explicitly state the template parameters.  A function template call can infer
> the template parameters and use them to instantiate a class instance.

Thanks. That makes sense ... I think.

Craig Dillabaugh:

>    foreach( idx, count; lockstep( iota!ubyte(ubyte.min,
> ubyte.max), bins ) )

Also note that doesn't iterate the whole ubyte range. Maybe we need another iota range for that, with a different name or with an optional template argument string like "[]" as std.random.uniform. Opinions welcome.

Bye,
bearophile

On Monday, 24 June 2013 at 14:33:48 UTC, bearophile wrote:
> Craig Dillabaugh:
>
>>   foreach( idx, count; lockstep( iota!ubyte(ubyte.min,
>> ubyte.max), bins ) )
>
> Also note that doesn't iterate the whole ubyte range. Maybe we need another iota range for that, with a different name or with an optional template argument string like "[]" as std.random.uniform. Opinions welcome.
>
> Bye,
> bearophile

Opps.  Of course.

The optional template argument sounds like a good idea.

Any idea why the original wouldn't compile though?

Craig

David:

> Something seems to be wrong with opApply of lockstep.
> Or maybe I miss something obvious...

I have suggested to remove lockstep from Phobos:
http://d.puremagic.com/issues/show_bug.cgi?id=8155

Why don't you try to use std.range.zip?

Bye,
bearophile

On Monday, 24 June 2013 at 14:56:41 UTC, bearophile wrote:
> David:
>
>> Something seems to be wrong with opApply of lockstep.
>> Or maybe I miss something obvious...
>
> I have suggested to remove lockstep from Phobos:
> http://d.puremagic.com/issues/show_bug.cgi?id=8155
>
> Why don't you try to use std.range.zip?
>
> Bye,
> bearophile

Funny you should mention that, I vaguely recalled you old thread,
and replaced lockstep with zip.

After making the following changes:

uint[ubyte.max - ubyte.min+1] bins;
  ...

foreach( e; zip( iota(ubyte.min, ubyte.max+1), bins ) )
{
    if(count > 0 ) {
	writeln("Bin = ", e[0], " count = ", e[1] );
    }
}

I now get the error (which seems to be the same problem I had
before - see the last error):

test.d(11): Error: template std.range.zip does not match any
function template declaration. Candidates are:
/usr/include/dmd/phobos/std/range.d(4451):
std.range.zip(Ranges...)(Ranges ranges) if (Ranges.length &&
allSatisfy!(isInputRange, Ranges))
/usr/include/dmd/phobos/std/range.d(4458):
std.range.zip(Ranges...)(StoppingPolicy sp, Ranges ranges) if
(Ranges.length && allSatisfy!(isInputRange, Ranges))
/usr/include/dmd/phobos/std/range.d(4451): Error: template
std.range.zip cannot deduce template function from argument types
!()(Result, uint[256LU])

Craig Dillabaugh:

> I now get the error (which seems to be the same problem I had
> before - see the last error):
> ...
> /usr/include/dmd/phobos/std/range.d(4451): Error: template
> std.range.zip cannot deduce template function from argument types
> !()(Result, uint[256LU])

Most range/algorithm functions unfortunately don't accept a fixes size array. So you have to slice it:

void main() {
    import std.stdio, std.range;

    ubyte[] data = [17, 32, 32, 32, 38, 39, 39, 47,
                    47, 47, 47, 109, 111, 111, 128];
    uint[ubyte.max - ubyte.min + 1] bins;

    foreach (immutable val; data)
        bins[val]++;

    foreach (uint idx, count; iota(ubyte.min, ubyte.max + 1).zip(bins[]))
        if (count > 0)
            writeln("Bin = ", idx, " count = ", count);
}

Bye,
bearophile

On Monday, 24 June 2013 at 15:15:46 UTC, bearophile wrote:
> Craig Dillabaugh:
>
>> clip
>
> Most range/algorithm functions unfortunately don't accept a fixes size array. So you have to slice it:
>
> void main() {
>     import std.stdio, std.range;
>
>     ubyte[] data = [17, 32, 32, 32, 38, 39, 39, 47,
>                     47, 47, 47, 109, 111, 111, 128];
>     uint[ubyte.max - ubyte.min + 1] bins;
>
>     foreach (immutable val; data)
>         bins[val]++;
>
>     foreach (uint idx, count; iota(ubyte.min, ubyte.max + 1).zip(bins[]))
>         if (count > 0)
>             writeln("Bin = ", idx, " count = ", count);
> }
>
> Bye,
> bearophile

Thanks.  Now it works, if I use .zip().