Re: Hash/Array slice : how to exclude items?

[Corion]

If this is only about the top-level items, I would create a shallow copy and delete the keys there (or only keep the "good" keys):

sub debug_hash( $hashref, $bad_keys = [qw[ schema logger ]] ) {
    my %output = %$hashref;
    delete @output{ @$bad_keys };
    print Dumper \%output;
}

debug_hash( { logger => 'foo', payload => 'bar' } );
debug_hash( { schema => 'users', password => 'hunter2' }, ['schema', '
+password'] );

[haukex]

I would create a shallow copy and delete the keys there

An alternative:

sub debug_hash ( $hashref, $bad_keys = [qw/ schema logger /] ) {
    delete local @$hashref{ @$bad_keys };
    print Dumper $hashref;
}

[choroba]

delete local requires 5.12 (as mentioned in the link you provided, too, I just think it's worth mentioning here).

[bliako]

delete local looks promising, thanks haukex and ikegami. If only delete returned the remaining hash. Shouldn't this work?: print Dumper(do { delete local  @$hashref{ @$bad_keys }, $hashref} ); or this print Dumper(do { delete local  @$hashref{ @$bad_keys }; $hashref} ); My intention is to delete the elements of the local hash, pass that to Dumper and hopefully leave it untouched when Dumper returns.

my @unwanted = qw( schema log );
my %hash = (schema=>1, log=>2, aa=>3);
print Dumper(delete local @hash{ @unwanted }, \%hash);
print Dumper(\%hash);

$VAR1 = 1;
$VAR2 = 2;
$VAR3 = {
          'aa' => 3
        };
$VAR1 = {
          'aa' => 3
        };

my @unwanted = qw( schema log );
my %hash = (schema=>1, log=>2, aa=>3);
print Dumper(do { delete local @hash{ @unwanted }; \%hash });
print Dumper(\%hash);
$VAR1 = {
          'aa' => 3,
          'log' => 2,
          'schema' => 1
        };
$VAR1 = {
          'aa' => 3,
          'log' => 2,
          'schema' => 1
        };

[hv]

delete returns the thing(s) deleted, not the things remaining after deletion, so that idea won't fly.

The effect of local is undone at the end of the block (scope) in which it was done, so your proposed examples cannot work - the elements have already been restored by the time Dumper() gets a look at the hash.

If you can put the Dumper() call inside the block, then it will work:

  print do { delete local @$hashref{ @$bad_keys }; Dumper($hashref) };

For a complete example:

% perl -we '%a=(schema=>1,log=>2,aa=>3); use Data::Dumper;
  print do { delete local @a{qw{ schema log }}; Dumper(\%a) }'
$VAR1 = {
          'aa' => 3
        };
%

[LanX]

> Shouldn't this work?:

> print Dumper(do { delete local  @$hashref{ @$bad_keys }, $hashref} ); or this print Dumper(do { delete local  @$hashref{ @$bad_keys }; $hashref} );

yes it's surprising.

One needs to remember that local is protecting certain entries and not the whole hash (The hash could be a lexical variable, local wouldn't do anyway)

Since you are returning a reference, you'll see the restored entries again after leaving the block.

consider what's happening without delete

  DB<91> use Data::Dump qw/pp/ 

  DB<92> ; {local @hash{qw/log schema/};say pp \%hash}; say pp \%hash
{ a => 1, b => 2, c => 3, log => undef, schema => undef }
{ a => 1, b => 2, c => 3, log => "l", schema => "s" }

you can still have the desired effect by just returning a list or a new anonymous hash

  DB<96>  say pp do {delete local @hash{qw/log schema/}; %hash }; say 
+pp \%hash
("a", 1, "c", 3, "b", 2)
{ a => 1, b => 2, c => 3, log => "l", schema => "s" }

  DB<97>  say pp do {delete local @hash{qw/log schema/}; +{%hash} }; s
+ay pp \%hash
{ a => 1, b => 2, c => 3 }
{ a => 1, b => 2, c => 3, log => "l", schema => "s" }

  DB<98>

if you shy away from the overhead to return a new hash, just do the dumping inside the block.

  DB<99> ; {delete local @hash{qw/log schema/};say pp \%hash}; say pp 
+\%hash
{ a => 1, b => 2, c => 3 }
{ a => 1, b => 2, c => 3, log => "l", schema => "s" }

  DB<100>

HTH! :)