Filtering Associative Array Key-Values the D way

[David DeWitt via Digitalmars-d-learn]

I'm trying to understand filtering an Associative Array the D 
way.  I have the code below
(Using while readln cause problem failing on Debian using 
byLineCopy()).  When the byKeyValue().filter evaluates to reduce 
the number of Keys:Values to only the ones in the filtered 
header, what is the best way to transform the Pair back to an AA 
instead of having to run the foreach loop after?  Basically if 
the file has 300 columns and 300 in the full header but only 15 
in the filtered header I want the return of rec to only be the 15 
in an Associative Array.  Thanks :)



string line;
string[string][] records;
while ((line = f.readln()) !is null){
string[string] record;
auto rec = assocArray(zip(h1.fullHeader, 
splitter(line,',')))

.byKeyValue().filter!(a=h1.filteredHeader.canFind(a.key));


foreach(r;rec){
record[r.key] = r.value;
}
records ~= record;
}

Re: Filtering Associative Array Key-Values the D way

[Ali Çehreli via Digitalmars-d-learn]

On 06/24/2015 09:08 AM, David DeWitt wrote:

I'm trying to understand filtering an Associative Array the D way.  I
have the code below
(Using while readln cause problem failing on Debian using
byLineCopy()).  When the byKeyValue().filter evaluates to reduce the
number of Keys:Values to only the ones in the filtered header, what is
the best way to transform the Pair back to an AA instead of having to
run the foreach loop after?  Basically if the file has 300 columns and
300 in the full header but only 15 in the filtered header I want the
return of rec to only be the 15 in an Associative Array.  Thanks :)


 string line;
 string[string][] records;
 while ((line = f.readln()) !is null){
 string[string] record;
 auto rec = assocArray(zip(h1.fullHeader, splitter(line,',')))
.byKeyValue().filter!(a=h1.filteredHeader.canFind(a.key));

 foreach(r;rec){
 record[r.key] = r.value;
 }
 records ~= record;
 }


It would be more efficient to filter the input before creating a larger 
AA to be thrown away:


import std.stdio;
import std.range;
import std.algorithm;

void main()
{
auto keys = 10.iota;
auto values = keys.map!(k = 10 * k);

auto result = zip(keys, values)
  .filter!(t = t[0] % 2)
  .assocArray;

writefln(%(%s: %s\n%), result);
}

The AA contains elements with odd keys:

1: 10
5: 50
9: 90
3: 30
7: 70

Ali