Re^2: What is the easiest way to merge two hashes?

For the unnested case this code can determine the joined set of keys of two hash references given the keys of the two hash references separately:

use Data::Dumper;

my $hash1 = {
    common_key => 'foo',
    hash1_specific_key => 'some value'
};

my $hash2 = {
    common_key => 'bar',
    hash2_specific_key => 'some other value'
};

my $joined_keys = [ keys( %{ {
    map { $_=>undef }  keys( %{$hash1} ) , keys( %{$hash2} ) 
} } ) ];

print Data::Dumper->Dump([$joined_keys],['joined keys']);
[download]

Outputs:

$joined keys = [
                 'hash2_specific_key',
                 'common_key',
                 'hash1_specific_key'
               ];
[download]

Comment on Re^2: What is the easiest way to merge two hashes? Select or Download Code

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Re^3: What is the easiest way to merge two hashes? by BrowserUk (Patriarch) on Feb 15, 2015 at 11:14 UTC
this code can determine the joined set of keys of two hash references given the keys of the two hash references separately So does this, rather more simply: `sub mergedHashKeys{ my( $r1, $r2 ) = @_; my %h = ( %{ $r1 }, %{ $r2 } ); return [ keys %h ]; };; $hash1 = { common_key => 'foo', hash1_specific_key => 'some value' };; $hash2 = { common_key => 'bar', hash2_specific_key => 'some other value' };; pp mergedHashKeys( $hash1, $hash2 );; ["hash2_specific_key", "common_key", "hash1_specific_key"]` [download] Or if you are into programming in hieroglyphics, just: `sub mergedHashKeys{ [ keys %{{ %{ $_[0] }, %{ $_[1] } }} ] };;` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I'm with torvalds on this In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked	[reply] [d/l] [select]
Re^4: What is the easiest way to merge two hashes? by tkguifan (Scribe) on Feb 15, 2015 at 14:30 UTC
For this you have to create the image of the merged hash in memory. If you have incredibly large data structures ( as I do ) this may be a wasting of resources ( in the extreme case this can cause the program to run out of memory ). In may solution it is enough to query the keys of both hashes without ever creating the merged hash itself.	[reply]
Re^5: What is the easiest way to merge two hashes? by BrowserUk (Patriarch) on Feb 15, 2015 at 16:37 UTC
In may solution it is enough to query the keys of both hashes without ever creating the merged hash itself. Sorry, but that is rubbish. This code: `my $joined_keys = [ keys( %{ { map { $_=>undef } keys( %{$hash1} ) , keys( %{$hash2} ) +} } ) ]; # This.....^.......................................................... +..^ is a hash built from #...............................^^^^^^^^^^^^^^^^^...^^^^^^^^^^^^^^ #...the combined (potentially huge) lists of the keys from both hashes + PLUS #.....................^^^^^...undef as the value for each key in the c +ombined list...` [download] And is functionally and memory consumption-wise, nearly identical to this code: `sub mergedHashKeys{ [ keys %{ { %{ $_[0] }, %{ $_[1] } + } } ] };;` [download] And, your code creates two (potentially) huge lists; one going into the map and one coming out that is twice as long; from which the combined hash is constructed. Any memory savings will be minimal. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I'm with torvalds on this In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked	[reply] [d/l] [select]