Re^2: Possible for Map to create Hash of Hash?

Thanks Rolf. This answered what I was trying to do achieve with map. I was hoping to be able to declare and initiate %hash in one line but couldn't get it to work because of the collision and couldn't be sure if it was possible.

 You can't have map returning nested hashes assigned to a top-level ha
+sh, otherwise entries from different lines would collide (2 x Sidney,
+ 2 x Canberra)

 my %hash = map { entry1 => { entry2 => 1} } <> # collisions of entry1
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Re^3: Possible for Map to create Hash of Hash? by LanX (Saint) on May 11, 2013 at 13:39 UTC
> couldn't be sure if it was possible. Well, I think the point is that `map` isn't primarily meant to operate on hashes, it takes a list and returns a list. `LIST = map {BLOCK} LIST` But assigning a list to a hash can result in collisions `DB<166> %hash = (Canberra => { 12 => 1}, Canberra => { 18 => 1} ) => ("Canberra", { 18 => 1 })` [download] You could however design a `sub join_deep` , such that: `DB<178> sub join_deep { my %hash; while ( my ($a,$b) = splice @_,0,2 ) { $hash{$a}= { %{$hash{$a}}, %$b } } return %hash; } DB<179> %h =join_deep (Canberra => { 12 => 1}, Canberra => { 18 => 1 +} ) => ("Canberra", { 12 => 1, 18 => 1 })` [download] But frankly, I don't see the need for such abstraction. Cheers Rolf ( addicted to the Perl Programming Language) couldn't be sure if it was possible.	[reply] [d/l] [select]

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Re^3: Possible for Map to create Hash of Hash?
by LanX (Saint) on May 11, 2013 at 13:39 UTC

> couldn't be sure if it was possible.

Well, I think the point is that map isn't primarily meant to operate on hashes, it takes a list and returns a list.

LIST = map {BLOCK} LIST

But assigning a list to a hash can result in collisions

  DB<166> %hash = (Canberra => { 12 => 1}, Canberra => { 18 => 1} )
 => ("Canberra", { 18 => 1 })
[download]

You could however design a sub join_deep , such that:

  DB<178> sub join_deep {
             my %hash;
             while ( my ($a,$b) = splice @_,0,2 ) {
                $hash{$a}= { %{$hash{$a}}, %$b }
             }
             return %hash;
          }

  DB<179> %h =join_deep (Canberra => { 12 => 1}, Canberra => { 18 => 1
+} )
 => ("Canberra", { 12 => 1, 18 => 1 })
[download]

But frankly, I don't see the need for such abstraction.

Cheers Rolf

( addicted to the Perl Programming Language) couldn't be sure if it was possible.

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