digitalmars.D.learn - Test for element in array

Paolo Invernizzi (11/11) Jul 13 2006 Hi all,

BCS (13/29) Jul 13 2006 import std.stdio;

Dave (4/38) Jul 13 2006 That's a very elegant solution and it should work, but according to my

BCS (9/53) Jul 13 2006 Bizarre

Kirk McDonald (6/71) Jul 13 2006 Hmmm. "Lambda properties." Fun.
Andrei Khropov (3/4) Jul 13 2006 Yeah, this new delegate syntax is cool !

Don Clugston (4/9) Jul 14 2006 Wow! I didn't know you could have a naked {} like that as a void

BCS (3/17) Jul 14 2006 Not quite naked, without the ending () the type is "bool delegate(void)"...

Lars Ivar Igesund (8/26) Jul 14 2006 The () is for calling it, {} is fine if you want pass (what I would call

Dave (2/63) Jul 13 2006 Ah... Thanks.

Andrei Khropov (4/20) Jul 13 2006 Despite BCS proposed a cool solution I think 'in' should be built-in for...

BCS (8/34) Jul 13 2006 the semantics are backwards, not a killer but its a little inconsistent.

Regan Heath (19/50) Jul 13 2006 True.. (wild idea alert) unless we make it valid to index an array with ...
Paolo Invernizzi (6/15) Jul 14 2006 I would be satisfied also if it just returns a boolean value, like a

Chris Nicholson-Sauls (23/44) Jul 14 2006 That's most likely the best solution for the moment. Although, you coul...

Ivan Senji (9/42) Jul 14 2006 Yeah, some think it is some think it isn't, I think it isn't but it is

Andrei Khropov (6/16) Jul 14 2006 AA is also often called dictionary or map (in STL for example).

BCS (12/32) Jul 14 2006 How about allow void[TYPE]? No values, only keys.

Carlos Santander (8/53) Jul 14 2006 It was possible some time ago, but it got forbidden. What I've been doin...

Derek Parnell (9/14) Jul 14 2006 =

Kirk McDonald (12/32) Jul 14 2006 You can also have a sort of poor-man's multiset with:

Paolo Invernizzi (9/23) Jul 15 2006 That's what I liked from python... with dicts (aka AA) and lists (aka

Paolo Invernizzi <arathorn NOSPAM_fastwebnet.it> writes:

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

Jul 13 2006

BCS <BCS pathlink.com> writes:

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");
}

Jul 13 2006

Dave <Dave_member pathlink.com> writes:

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.

Jul 13 2006

BCS <BCS pathlink.com> writes:

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

Jul 13 2006

Kirk McDonald <kirklin.mcdonald gmail.com> writes:

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

Jul 13 2006

"Andrei Khropov" <andkhropov nospam_mtu-net.ru> writes:

BCS wrote:

  if({foreach(i;a) if(i==j) return true; return false;}())

Yeah, this new delegate syntax is cool !

--

Jul 13 2006

Don Clugston <dac nospam.com.au> writes:

Andrei Khropov wrote:
 BCS wrote:
 
  if({foreach(i;a) if(i==j) return true; return false;}())

 
 Yeah, this new delegate syntax is cool !

Wow! I didn't know you could have a naked {} like that as a void 
delegate. That is cool. Looks as though D has sucked all the juice out 
of C++, and is moving onto the scripting languages...

Jul 14 2006

BCS <BCS pathlink.com> writes:

Don Clugston wrote:
 Andrei Khropov wrote:
 
 BCS wrote:

  if({foreach(i;a) if(i==j) return true; return false;}())


 Yeah, this new delegate syntax is cool !

 
 
 Wow! I didn't know you could have a naked {} like that as a void 
 delegate. That is cool. Looks as though D has sucked all the juice out 
 of C++, and is moving onto the scripting languages...
 

Not quite naked, without the ending () the type is "bool delegate(void)" 
a.k.a. always true.

Jul 14 2006

Lars Ivar Igesund <larsivar igesund.net> writes:

BCS wrote:

 Don Clugston wrote:
 Andrei Khropov wrote:
 
 BCS wrote:

  if({foreach(i;a) if(i==j) return true; return false;}())


 Yeah, this new delegate syntax is cool !

 
 
 Wow! I didn't know you could have a naked {} like that as a void
 delegate. That is cool. Looks as though D has sucked all the juice out
 of C++, and is moving onto the scripting languages...
 

 
 Not quite naked, without the ending () the type is "bool delegate(void)"
 a.k.a. always true.

The () is for calling it, {} is fine if you want pass (what I would call
naked) a delegate to a function taking delegates as arguments.
 
-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource & #D: larsivi

Jul 14 2006

Dave <Dave_member pathlink.com> writes:

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.

Jul 13 2006

"Andrei Khropov" <andkhropov nospam_mtu-net.ru> writes:

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?


--

Jul 13 2006

BCS <BCS pathlink.com> writes:

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?

Jul 13 2006

"Regan Heath" <regan netwin.co.nz> writes:

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

Jul 13 2006

Paolo Invernizzi <arathorn NOSPAM_fastwebnet.it> writes:

BCS wrote:

 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?

I would be satisfied also if it just returns a boolean value, like a 
simple inclusion test...

But for now, I will use the BCS solutions! Thanks!

---
Paolo

Jul 14 2006

Chris Nicholson-Sauls <ibisbasenji gmail.com> writes:

Paolo Invernizzi wrote:
 BCS wrote:
 
 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?

 
 
 I would be satisfied also if it just returns a boolean value, like a 
 simple inclusion test...
 
 But for now, I will use the BCS solutions! Thanks!
 
 ---
 Paolo
 

That's most likely the best solution for the moment.  Although, you could
generalize it by 
  taking advantage of IFTI and defining this somewhere:















Then your test would just be:





I think it reads pretty well, even if it isn't quite as "clean" as (bar in foo)
in 
comparison.  Which, incidentally, also does read well.

-- Chris Nicholson-Sauls

Jul 14 2006

Ivan Senji <ivan.senji_REMOVE_ _THIS__gmail.com> writes:

BCS 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.

Yeah, some think it is some think it isn't, I think it isn't but it is 
an old discussion and probably one we will never agree on.

IMO:
normal arrays store *values* which are indexed by a key (index)
associative arrays store *keys* and the value is just an additional 
information about the key.

That is only my opinion as some people think that AA's also are about 
values.

Jul 14 2006

"Andrei Khropov" <andkhropov nospam_mtu-net.ru> writes:

Ivan Senji wrote:

 
 Yeah, some think it is some think it isn't, I think it isn't but it is an old
 discussion and probably one we will never agree on.
 
 IMO:
 normal arrays store values which are indexed by a key (index)
 associative arrays store keys and the value is just an additional information
 about the key.
 
 That is only my opinion as some people think that AA's also are about values.

AA is also often called dictionary or map (in STL for example).

If you speak about some kind of collection where only value (and its presense
or absense in the collection) is important it's probably better to call it a
set.

--

Jul 14 2006

BCS <BCS pathlink.com> writes:

Andrei Khropov wrote:
 Ivan Senji wrote:
 
 
Yeah, some think it is some think it isn't, I think it isn't but it is an old
discussion and probably one we will never agree on.

IMO:
normal arrays store values which are indexed by a key (index)
associative arrays store keys and the value is just an additional information
about the key.

That is only my opinion as some people think that AA's also are about values.

 
 
 AA is also often called dictionary or map (in STL for example).
 
 If you speak about some kind of collection where only value (and its presense
 or absense in the collection) is important it's probably better to call it a
 set.
 

How about allow void[TYPE]? No values, only keys.

void[char[]] whos;

... // fill whos

if("Bob" in whos) Hire("Bob");
if("Capone" in whos) whos.remove("Capone");
whos["Bubba"];	// add Bubba

auto him = whos["Bubba"];	// can't do that with a void

// ( or

auto him = whos["Bubba"];	// == bool.true
auto who = whos["Capone"];	// == bool.false

// )

Jul 14 2006

Carlos Santander <csantander619 gmail.com> writes:

BCS escribi�:
 Andrei Khropov wrote:
 Ivan Senji wrote:


 Yeah, some think it is some think it isn't, I think it isn't but it 
 is an old
 discussion and probably one we will never agree on.

 IMO:
 normal arrays store values which are indexed by a key (index)
 associative arrays store keys and the value is just an additional 
 information
 about the key.

 That is only my opinion as some people think that AA's also are about 
 values.


 AA is also often called dictionary or map (in STL for example).

 If you speak about some kind of collection where only value (and its 
 presense
 or absense in the collection) is important it's probably better to 
 call it a
 set.

 
 How about allow void[TYPE]? No values, only keys.
 
 void[char[]] whos;
 
 .... // fill whos
 
 if("Bob" in whos) Hire("Bob");
 if("Capone" in whos) whos.remove("Capone");
 whos["Bubba"];    // add Bubba
 
 auto him = whos["Bubba"];    // can't do that with a void
 
 // ( or
 
 auto him = whos["Bubba"];    // == bool.true
 auto who = whos["Capone"];    // == bool.false
 
 // )

It was possible some time ago, but it got forbidden. What I've been doing (and
I 
think others too) is:

char [] [char []] whos;

And set the element to both the key and the value. However, I admit I liked
void 
[T].

-- 
Carlos Santander Bernal

Jul 14 2006

"Derek Parnell" <derek psych.ward> writes:

On Sat, 15 Jul 2006 02:46:24 +1000, Carlos Santander  =

<csantander619 gmail.com> wrote:


 It was possible some time ago, but it got forbidden. What I've been  =

 doing (and I think others too) is:

 char [] [char []] whos;

 And set the element to both the key and the value. However, I admit I =

 =

 liked void [T].

Actually I use

   bool[ char[] ] whos;

   whos["Capone"] =3D true;



-- =

Derek Parnell
Melbourne, Australia

Jul 14 2006

Kirk McDonald <kirklin.mcdonald gmail.com> writes:

Derek Parnell wrote:
 On Sat, 15 Jul 2006 02:46:24 +1000, Carlos Santander  
 <csantander619 gmail.com> wrote:
 
 
 It was possible some time ago, but it got forbidden. What I've been  
 doing (and I think others too) is:

 char [] [char []] whos;

 And set the element to both the key and the value. However, I admit I  
 liked void [T].

 
 
 Actually I use
 
   bool[ char[] ] whos;
 
   whos["Capone"] = true;
 

You can also have a sort of poor-man's multiset with:

int[ char[] ] ms;

One could easily wrap this with a more multiset-ish interface, but to 
add an item you just say:

++ms["moo"];

And to remove:

if (--ms["moo"] <= 0) ms.remove("moo");

-- 
Kirk McDonald
Pyd: Wrapping Python with D
http://dsource.org/projects/pyd/wiki

Jul 14 2006

Paolo Invernizzi <arathorn NOSPAM_fastwebnet.it> writes:

Kirk McDonald wrote:
 Derek Parnell wrote:
 You can also have a sort of poor-man's multiset with:
 
 int[ char[] ] ms;
 
 One could easily wrap this with a more multiset-ish interface, but to 
 add an item you just say:
 
 ++ms["moo"];
 
 And to remove:
 
 if (--ms["moo"] <= 0) ms.remove("moo");
 

That's what I liked from python... with dicts (aka AA) and lists (aka 
arrays) you can have basically every container you want.

And some newbie reading the code can grasp the meaning without loosing 
himself in a plethora of containers...

Now python users are complaining against too much features added in the 
language...

---
Paolo

Jul 15 2006

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digitalmars.D.learn - Test for element in array