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reply Johnny <bierbauch jenz.info> writes:
Hello,

I've got a problem. I need to check if a hash key exists in a for loop like:

int [char[]] a;
int [char[]] b;

a = { a => 1; b => 5; c=> 8 }
b = { a => 5; b => 4; d => 3; f => 4 }

foreach (m; a.keys) {
  if ( b[m] ) {
   writefln("%s %s %s", m, a[m], b[m])
  }
  else {
    writefln("%s %s", m, a[m])
  }
}

... not "real" D but I hope you understand the code and what it should do.
Thanks.
Apr 18 2007
next sibling parent reply BCS <BCS pathlink.com> writes:
Johnny wrote:

 Hello,
 
 I've got a problem. I need to check if a hash key exists in a for loop like:
 
 int [char[]] a;
 int [char[]] b;
 
 a = { a => 1; b => 5; c=> 8 }
 b = { a => 5; b => 4; d => 3; f => 4 }
 
 foreach (m; a.keys) {
   if ( b[m] ) {
    writefln("%s %s %s", m, a[m], b[m])
   }
   else {
     writefln("%s %s", m, a[m])
   }
 }
 
 ... not "real" D but I hope you understand the code and what it should do.
 Thanks.
 


What is the issue? That's about as good as anything I can think of. You 
might try this (but it's not much better)

foreach (k, v1; a) {
   if ( auto v2 = k in b )	// is this what your looking for?
    writefln("%s %s %s", k, v1, *v2)
   else
    writefln("%s %s", k, v1)
}
Apr 18 2007
parent reply Johnny <bierbauch jenz.info> writes:
BCS Wrote:


 Johnny wrote:

 Hello,
 
 I've got a problem. I need to check if a hash key exists in a for loop like:
 
 int [char[]] a;
 int [char[]] b;
 
 a = { a => 1; b => 5; c=> 8 }
 b = { a => 5; b => 4; d => 3; f => 4 }
 
 foreach (m; a.keys) {
   if ( b[m] ) {
    writefln("%s %s %s", m, a[m], b[m])
   }
   else {
     writefln("%s %s", m, a[m])
   }
 }
 
 ... not "real" D but I hope you understand the code and what it should do.
 Thanks.
 


 
 What is the issue? That's about as good as anything I can think of. You 
 might try this (but it's not much better)
 
 foreach (k, v1; a) {
    if ( auto v2 = k in b )	// is this what your looking for?
     writefln("%s %s %s", k, v1, *v2)
    else
     writefln("%s %s", k, v1)
 }


A good hint. my problem is that I get an ArrayBounds error if i try it with my
method.
... an I can't catch it
Apr 18 2007
parent reply BCS <BCS pathlink.com> writes:
Johnny wrote:

 BCS Wrote:

Johnny wrote:


foreach (m; a.keys) {
  if ( b[m] ) {
   writefln("%s %s %s", m, a[m], b[m])
  }
  else {
    writefln("%s %s", m, a[m])
  }
}


foreach (k, v1; a) {
   if ( auto v2 = k in b )	// is this what your looking for?
    writefln("%s %s %s", k, v1, *v2)
   else
    writefln("%s %s", k, v1)
}


 
 A good hint. my problem is that I get an ArrayBounds error if i try it with my
method.
 ... an I can't catch it


The "/a/ in /b/" construct fixes that. Just looking up the value should 
do what you described if the value isn't their.
Apr 18 2007
parent reply Johnny <bierbauch jenz.info> writes:
BCS Wrote:


 Johnny wrote:

 BCS Wrote:

Johnny wrote:




  >>

foreach (m; a.keys) {
  if ( b[m] ) {
   writefln("%s %s %s", m, a[m], b[m])
  }
  else {
    writefln("%s %s", m, a[m])
  }
}


foreach (k, v1; a) {
   if ( auto v2 = k in b )	// is this what your looking for?
    writefln("%s %s %s", k, v1, *v2)
   else
    writefln("%s %s", k, v1)
}


 
 A good hint. my problem is that I get an ArrayBounds error if i try it with my
method.
 ... an I can't catch it


 
 The "/a/ in /b/" construct fixes that. Just looking up the value should 
 do what you described if the value isn't their.


I've tested it, and yes thank you very much it works fine!
.. but still don't really understand what "auto v2 = m in b" means
something like v2 = b.keys ?
Apr 18 2007
parent BCS <BCS pathlink.com> writes:
Johnny wrote:

 BCS Wrote:
 
 

Johnny wrote:


BCS Wrote:


Johnny wrote:









foreach (m; a.keys) {
 if ( b[m] ) {
  writefln("%s %s %s", m, a[m], b[m])
 }
 else {
   writefln("%s %s", m, a[m])
 }
}


foreach (k, v1; a) {
  if ( auto v2 = k in b )	// is this what your looking for?
   writefln("%s %s %s", k, v1, *v2)
  else
   writefln("%s %s", k, v1)
}


A good hint. my problem is that I get an ArrayBounds error if i try it with my
method.
... an I can't catch it


The "/a/ in /b/" construct fixes that. Just looking up the value should 
do what you described if the value isn't their.


 
 
 I've tested it, and yes thank you very much it works fine!
 .. but still don't really understand what "auto v2 = m in b" means
 something like v2 = b.keys ?
 


actualy its about three cool features in one line

here is the slightly expanded vertion

foreach (k, v1; a)
{
   int* v2 = k in b;
	// return a pointer to the value assigned to key k in b

   if (v2 !is null )
	// if pointer is not null (key exists)
    writefln("%s %s %s", k, v1, *v2)
   else
	// if pointer is null (key dosn't exist)
    writefln("%s %s", k, v1)
}

the vertion I used uses type inference to avoid needing to know the type 
and also uses the "declare and check a variable" feature.

http://www.digitalmars.com/d/expression.html#InExpression

http://www.digitalmars.com/d/statement.html#IfStatement
   look for IfCondition and Declarator



 Apr 18 2007



prev sibling  parent  Derek Parnell <derek psych.ward>  writes:


On Wed, 18 Apr 2007 12:13:39 -0400, Johnny wrote:


 Hello,
 
 I've got a problem. I need to check if a hash key exists in a for loop like:
 
 int [char[]] a;
 int [char[]] b;
 
 a = { a => 1; b => 5; c=> 8 }
 b = { a => 5; b => 4; d => 3; f => 4 }
 
 foreach (m; a.keys) {
   if ( b[m] ) {
    writefln("%s %s %s", m, a[m], b[m])
   }
   else {
     writefln("%s %s", m, a[m])
   }
 }
 
 ... not "real" D but I hope you understand the code and what it should do.
 Thanks.


Try replacing "if (b[m])" with "if (m in b)".

The correct way to find out if a specific key exists in an AA is to use the
"in" syntax. 

-- 
Derek Parnell
Melbourne, Australia
"Justice for David Hicks!"
skype: derek.j.parnell



 Apr 18 2007