Test for element in array

Hi all, Someone can suggest me the best way for testing the presence of an element in an array? Coming from python, something like... if( x in array_of_x && y in array_of_y ){ ... } The workaround, apart from using a simple 'for' loop, is to use an associative array, and test for key... --- Paolo

Paolo Invernizzi wrote: > Hi all, > > Someone can suggest me the best way for testing the presence of an element in an array? > > Coming from python, something like... > > if( x in array_of_x && y in array_of_y ){ > ... > } > > The workaround, apart from using a simple 'for' loop, is to use an associative array, and test for key... > > --- > Paolo import std.stdio; void main() { int[] a = new int[10]; int j=1; // populate a foreach(int i, inout int k; a) k=i; if({foreach(i;a) if(i==j) return true; return false;}) writef("true\n"); else writef("false\n"); }

BCS wrote: > Paolo Invernizzi wrote: >> Hi all, >> >> Someone can suggest me the best way for testing the presence of an element in an array? >> >> Coming from python, something like... >> >> if( x in array_of_x && y in array_of_y ){ >> ... >> } >> >> The workaround, apart from using a simple 'for' loop, is to use an associative array, and test for key... >> >> --- >> Paolo > > > import std.stdio; > > void main() > { > int[] a = new int[10]; > int j=1; > > // populate a > foreach(int i, inout int k; a) k=i; > > if({foreach(i;a) if(i==j) return true; return false;}) > writef("true\n"); > else > writef("false\n"); > } That's a very elegant solution and it should work, but according to my tests it doesn't (darn). It never returns false. Set j = 100 once and give it a try.

Dave wrote: > BCS wrote: > >> Paolo Invernizzi wrote: >> >>> Hi all, >>> >>> Someone can suggest me the best way for testing the presence of an element in an array? >>> >>> Coming from python, something like... >>> >>> if( x in array_of_x && y in array_of_y ){ >>> ... >>> } >>> >>> The workaround, apart from using a simple 'for' loop, is to use an associative array, and test for key... >>> >>> --- >>> Paolo >> >> >> >> import std.stdio; >> >> void main() >> { >> int[] a = new int[10]; >> int j=1; >> >> // populate a >> foreach(int i, inout int k; a) k=i; >> >> if({foreach(i;a) if(i==j) return true; return false;}) >> writef("true\n"); >> else >> writef("false\n"); >> } > > > That's a very elegant solution and it should work, but according to my tests it doesn't (darn). It never returns false. > > Set j = 100 once and give it a try. Bizarre -- if({foreach(i;a) if(i==j) return true; return false;}) ++ if({foreach(i;a) if(i==j) return true; return false;}()) this fixes it. WT... Oh. {return false;}.typeof == bool delegate() {return false;}().typeof == bool

BCS wrote: > Dave wrote: > >> BCS wrote: >> >>> Paolo Invernizzi wrote: >>> >>>> Hi all, >>>> >>>> Someone can suggest me the best way for testing the presence of an element in an array? >>>> >>>> Coming from python, something like... >>>> >>>> if( x in array_of_x && y in array_of_y ){ >>>> ... >>>> } >>>> >>>> The workaround, apart from using a simple 'for' loop, is to use an associative array, and test for key... >>>> >>>> --- >>>> Paolo >>> >>> >>> >>> >>> import std.stdio; >>> >>> void main() >>> { >>> int[] a = new int[10]; >>> int j=1; >>> >>> // populate a >>> foreach(int i, inout int k; a) k=i; >>> >>> if({foreach(i;a) if(i==j) return true; return false;}) >>> writef("true\n"); >>> else >>> writef("false\n"); >>> } >> >> >> >> That's a very elegant solution and it should work, but according to my tests it doesn't (darn). It never returns false. >> >> Set j = 100 once and give it a try. > > > Bizarre > > -- if({foreach(i;a) if(i==j) return true; return false;}) > ++ if({foreach(i;a) if(i==j) return true; return false;}()) > > this fixes it. > > WT... > > Oh. > > {return false;}.typeof == bool delegate() > {return false;}().typeof == bool > > Hmmm. "Lambda properties." Fun. -- Kirk McDonald Pyd: Wrapping Python with D http://dsource.org/projects/pyd/wiki

Paolo Invernizzi wrote: > Hi all, > > Someone can suggest me the best way for testing the presence of an element in an array? > > Coming from python, something like... > > if( x in array_of_x && y in array_of_y ){ > ... > } > > The workaround, apart from using a simple 'for' loop, is to use an associative array, and test for key... > > --- > Paolo Despite BCS proposed a cool solution I think 'in' should be built-in for usual (non-associative) arrays too. why not? --

Andrei Khropov wrote: > Paolo Invernizzi wrote: > > >>Hi all, >> >>Someone can suggest me the best way for testing the presence of an element in >>an array? >> >>Coming from python, something like... >> >>if( x in array_of_x && y in array_of_y ){ >> ... >>} >> >>The workaround, apart from using a simple 'for' loop, is to use an >>associative array, and test for key... >> >>--- >>Paolo > > > Despite BCS proposed a cool solution thanks > I think 'in' should be built-in for usual (non-associative) arrays too. why not? > > the semantics are backwards, not a killer but its a little inconsistent. With aa, the type of the LHS is the type of the index if(a in b) b[a]; // valid with non-aa, the type of the LHS would be the type of the stored value. The above wont always work for a non-aa. Also which a in b is found? The first? An array of all? The last?

BCS wrote: > Dave wrote: >> BCS wrote: >> >>> Paolo Invernizzi wrote: >>> >>>> Hi all, >>>> >>>> Someone can suggest me the best way for testing the presence of an element in an array? >>>> >>>> Coming from python, something like... >>>> >>>> if( x in array_of_x && y in array_of_y ){ >>>> ... >>>> } >>>> >>>> The workaround, apart from using a simple 'for' loop, is to use an associative array, and test for key... >>>> >>>> --- >>>> Paolo >>> >>> >>> >>> import std.stdio; >>> >>> void main() >>> { >>> int[] a = new int[10]; >>> int j=1; >>> >>> // populate a >>> foreach(int i, inout int k; a) k=i; >>> >>> if({foreach(i;a) if(i==j) return true; return false;}) >>> writef("true\n"); >>> else >>> writef("false\n"); >>> } >> >> >> That's a very elegant solution and it should work, but according to my tests it doesn't (darn). It never returns false. >> >> Set j = 100 once and give it a try. > > Bizarre > > -- if({foreach(i;a) if(i==j) return true; return false;}) > ++ if({foreach(i;a) if(i==j) return true; return false;}()) > > this fixes it. > > WT... > > Oh. > > {return false;}.typeof == bool delegate() > {return false;}().typeof == bool > > Ah... Thanks.

July 14, 2006

Re: Test for element in array

Posted by Regan Heath
in reply to BCS

Permalink

Regan Heath

Posted in reply to BCS

Permalink

On Thu, 13 Jul 2006 16:46:46 -0700, BCS <BCS@pathlink.com> wrote:
> Andrei Khropov wrote:
>> Paolo Invernizzi wrote:
>>
>>> Hi all,
>>>
>>> Someone can suggest me the best way for testing the presence of an element in
>>> an array?
>>>
>>> Coming from python, something like...
>>>
>>> if( x in array_of_x && y in array_of_y ){
>>>   ...
>>> }
>>>
>>> The workaround, apart from using a simple 'for' loop, is to use an
>>> associative array, and test for key...
>>>
>>> ---
>>> Paolo
>>   Despite BCS proposed a cool solution
>
> thanks
>
>> I think 'in' should be built-in for usual (non-associative) arrays too. why not?
>>
>
> the semantics are backwards, not a killer but its a little inconsistent.
>
> With aa, the type of the LHS is the type of the index
>
> if(a in b) b[a]; // valid
>
> with non-aa, the type of the LHS would be the type of the stored value.

True.. (wild idea alert) unless we make it valid to index an array with a value, which in turn returns the index of that value. It would perform a linear search from start to end (or match) therefore returning the 'first' match.

> The above wont always work for a non-aa. Also which a in b is found? The first? An array of all? The last?

In the case of 'in' aren't you just asking "is it in there", in which case it could return the first, or last, doesn't really matter.

However, 'in' does return a pointer to the value .. I think returning the first is the least surprising, most useful thing to do. It would also be consistent with the index by value idea above.

So, if you want the last match you say:
  if (a in b.reverse)

and if you want the 2nd, 3rd, 4th etc
  p = (a in b);           //gets first
  p = (a in b[b[*p]..$]); //2nd
  p = (a in b[b[*p]..$]); //3rd
  p = (a in b[b[*p]..$]); //4th

funky! ;)

Regan

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