• someone (14/14) Jun 20 2021 I often need to iterate through a filtered collection
• =?UTF-8?Q?Ali_=c3=87ehreli?= (17/38) Jun 21 2021 Two options for byKey and byKeyValue:
• someone (4/19) Jun 23 2021 Like 'em both, very flexible indeed, I think there are a couple
• frame (6/20) Jun 21 2021 An associative array is not a range but a struct, so it is extra
• someone (2/8) Jun 21 2021 Crystal-clear. Thanks !
• wjoe (9/23) Jun 21 2021 something like this ?
• someone (5/13) Jun 21 2021 This seems really interesting :)
• Elronnd (8/10) Jun 21 2021 Here's how I would do it:
• Steven Schveighoffer (8/21) Jun 21 2021 Alternatively (if you're ok with this sort of thing):
• someone (17/18) Jun 21 2021 Indeed; in a few very-specific situations I usually write code
• someone (2/9) Jun 21 2021 almost the same

someone <someone somewhere.com> writes:

I often need to iterate through a filtered collection 
(associative array) as following:

```d
string strComputerIDunwanted = "WS2"; /// associative array key 
to exclude

foreach (strComputerID, udtComputer; udtComputers) { /// 
.remove!(a => a == strComputerIDunwanted) ... ?

    if (strComputerID != strComputerIDunwanted) {

       ...

    }

}
```

Is there a way to filter the collection at the foreach-level to 
avoid the inner if ?

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 6/20/21 8:59 PM, someone wrote:
 I often need to iterate through a filtered collection (associative=20
 array) as following:
=20
 ```d
 string strComputerIDunwanted =3D "WS2"; /// associative array key to ex=

clude
=20
 foreach (strComputerID, udtComputer; udtComputers) { /// ..remove!(a =3D=
=20
 a =3D=3D strComputerIDunwanted) ... ?
=20
  =C2=A0=C2=A0 if (strComputerID !=3D strComputerIDunwanted) {
=20
  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ...
=20
  =C2=A0=C2=A0 }
=20
 }
 ```
=20
 Is there a way to filter the collection at the foreach-level to avoid=20
 the inner if ?

Two options for byKey and byKeyValue:


import std;

void main() {
   auto aa =3D [ "WS2" : 42, "WS3" : 43 ];
   string strComputerIDunwanted =3D "WS2";
   foreach (key; aa.byKey.filter!(k =3D> k !=3D strComputerIDunwanted)) {=

     writeln(key, ' ', aa[key]);
   }

   // 't' is the tuple of key and value
   foreach (t; aa.byKeyValue.filter!(t =3D> t.key !=3D strComputerIDunwan=
ted)) {
     writeln(t.key, ' ', t.value);
   }
}

Ali

someone <someone somewhere.com> writes:

On Monday, 21 June 2021 at 08:31:16 UTC, Ali Çehreli wrote:

 Two options for byKey and byKeyValue:


 import std;

 void main() {
   auto aa = [ "WS2" : 42, "WS3" : 43 ];
   string strComputerIDunwanted = "WS2";
   foreach (key; aa.byKey.filter!(k => k != 
 strComputerIDunwanted)) {
     writeln(key, ' ', aa[key]);
   }

   // 't' is the tuple of key and value
   foreach (t; aa.byKeyValue.filter!(t => t.key != 
 strComputerIDunwanted)) {
     writeln(t.key, ' ', t.value);
   }
 }

Like 'em both, very flexible indeed, I think there are a couple 
of places I could implement this. Thanks for your good advice as 
usual Ali :) !

frame <frame86 live.com> writes:

On Monday, 21 June 2021 at 03:59:10 UTC, someone wrote:
 I often need to iterate through a filtered collection 
 (associative array) as following:

 ```d
 string strComputerIDunwanted = "WS2"; /// associative array key 
 to exclude

 foreach (strComputerID, udtComputer; udtComputers) { /// 
 .remove!(a => a == strComputerIDunwanted) ... ?

    if (strComputerID != strComputerIDunwanted) {

       ...

    }

 }
 ```

 Is there a way to filter the collection at the foreach-level to 
 avoid the inner if ?

An associative array is not a range but a struct, so it is extra 
work to create a range from the AA to apply range functions.

You can get a range from it by using something like 
std.array.byPair() but for this usage you would be better of with 
your own function or template.

someone <someone somewhere.com> writes:

On Monday, 21 June 2021 at 08:35:19 UTC, frame wrote:

 An associative array is not a range but a struct, so it is 
 extra work to create a range from the AA to apply range 
 functions.

 You can get a range from it by using something like 
 std.array.byPair() but for this usage you would be better of 
 with your own function or template.

Crystal-clear. Thanks !

wjoe <invalid example.com> writes:

On Monday, 21 June 2021 at 03:59:10 UTC, someone wrote:
 I often need to iterate through a filtered collection 
 (associative array) as following:

 ```d
 string strComputerIDunwanted = "WS2"; /// associative array key 
 to exclude

 foreach (strComputerID, udtComputer; udtComputers) { /// 
 .remove!(a => a == strComputerIDunwanted) ... ?

    if (strComputerID != strComputerIDunwanted) {

       ...

    }

 }
 ```

 Is there a way to filter the collection at the foreach-level to 
 avoid the inner if ?

something like this ?

``` D
import std.array;
import std.algorithm;

     udtComputers.byPair
         .filter!(p => p.key != strComputerIDunwanted)
         .each!( (p) { /* foreach body */ } );
```

someone <someone somewhere.com> writes:

On Monday, 21 June 2021 at 15:32:09 UTC, wjoe wrote:

 something like this ?

 ``` D
 import std.array;
 import std.algorithm;

     udtComputers.byPair
         .filter!(p => p.key != strComputerIDunwanted)
         .each!( (p) { /* foreach body */ } );
 ```

This seems really interesting :)

Almost three weeks with D and I still must learn a lot of things, 
there's a lot to :) !

Thanks for your tip !

Elronnd <elronnd elronnd.net> writes:

On Monday, 21 June 2021 at 03:59:10 UTC, someone wrote:
 Is there a way to filter the collection at the foreach-level to 
 avoid the inner if ?

Here's how I would do it:

foreach (k, v; coll) {
     if (k == unwanted) continue;
     ...
}

You still have an if, but the actual loop body doesn't have to be 
nested, so it's easy to follow the control flow.

Steven Schveighoffer <schveiguy gmail.com> writes:

On 6/21/21 5:00 PM, Elronnd wrote:
 On Monday, 21 June 2021 at 03:59:10 UTC, someone wrote:
 Is there a way to filter the collection at the foreach-level to avoid 
 the inner if ?

 
 Here's how I would do it:
 
 foreach (k, v; coll) {
      if (k == unwanted) continue;
      ...
 }
 
 You still have an if, but the actual loop body doesn't have to be 
 nested, so it's easy to follow the control flow.

Alternatively (if you're ok with this sort of thing):

foreach (k, v; coll) if (k != unwanted) {
}

It's actually visually shorter than doing the filter.

And the benefit to using the if statement over the filter wrapper is 
that the compiler has to do a lot less work.

-Steve

someone <someone somewhere.com> writes:

On Monday, 21 June 2021 at 22:08:56 UTC, Steven Schveighoffer 
wrote:

 It's actually visually shorter than doing the filter.

Indeed; in a few very-specific situations I usually write code 
like this since it allows me to concentrate on the task at hand 
and not on the details to access the needed data, but for the 
clarity of the example I reformatted my code :)

Same when I code RO properties for classes, I usually do:

```d
private pxxxWhatever1; public whatever()  property { return 
pxxxWhatever1; }
private pxxxWhatever2; public whatever()  property { return 
pxxxWhatever2; }
private pxxxWhatever3; public whatever()  property { return 
pxxxWhatever3; }
```

It is far easier to read large chunk of similar constructs 
alongside than one below the other, at least, to me.

someone <someone somewhere.com> writes:

On Monday, 21 June 2021 at 21:00:42 UTC, Elronnd wrote:
 Here's how I would do it:

 foreach (k, v; coll) {
     if (k == unwanted) continue;
     ...
 }

 You still have an if, but the actual loop body doesn't have to 
 be nested, so it's easy to follow the control flow.

almost the same