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

I suppose that you know that %hash{...} is a new slice syntax that returns the keys too, and that's your intention.

Regarding your syntax

> %hash{-'schema', -'log'}

Well "-" has a meaning in arrays, so I'd rather prefer something else like "!"

But this would get messy if the list also included non-negated elements,

%hash{'schema', -'log'} # WHAT???

so for the sake of a clean design one would rather do only one negation

%hash{! 'schema', 'log'}

I'm not aware of a built-in syntax to do this, but it's basically syntactic sugar for a grep, see demo in debugger

  DB<1> @hash{'schema','log',a..c}=('s','l',1..3)

  DB<2> x \%hash
0  HASH(0x3168da0)
   'a' => 1
   'b' => 2
   'c' => 3
   'log' => 'l'
   'schema' => 's'
  DB<3>  x +{ %hash{grep !/^schema|log$/, keys %hash } }  # Note °
0  HASH(0x32e09d8)
   'a' => 1
   'b' => 2
   'c' => 3
  DB<4>
[download]

I know you didn't want grep, but this offers many flexibilities, like dynamically deciding what to exclude.

Cheers Rolf
_{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :)

Wikisyntax for the Monastery}

°) the +{...} is just an anonymous hash for pairwise dump

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Re^2: Hash/Array slice : how to exclude items? by LanX (Saint) on Jan 24, 2023 at 14:34 UTC
you can also design your own pseudo-operator `->$exclude` `DB<7> $exclude = sub { my $href = shift; my $excl= join '\|', @_; r +eturn +{ %$href{ grep !/^$excl$/, keys %$href } } } DB<8> x $h_ref 0 HASH(0x3168da0) 'a' => 1 'b' => 2 'c' => 3 'log' => 'l' 'schema' => 's' DB<9> x $h_ref->$exclude(qw/log schema/) 0 HASH(0x32e1158) 'a' => 1 'b' => 2 'c' => 3 DB<10>` [download] Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^3: Hash/Array slice : how to exclude items? -- be careful of anchoring by pryrt (Abbot) on Jan 24, 2023 at 15:00 UTC
`x +{ %hash{grep !/^schema\|log$/, keys %hash } }` `$exclude = sub { my $href = shift; my $excl= join '\|', @_; return +{ %$href{ grep !/^$excl$/, keys %$href } } }` Noting, of course, that because there are no parentheses in either of these regex, the `^` anchor only applies to the first term in the alternation list, the `$` anchor only applies to the final term in the alternation list, and any intermediate terms will be completely unanchored, which means that it's likely to exclude more keys than you might think: therefore, running `->exclude(qw/log schema/)` will not necessarily match running `->exclude(qw/schema log/)` , depending on the keys of the hash, which may or may not have been the intention. DB<1> @hash{'schema','log',a..c, 'schematic', 'blog'}=('s','l',1..3, +'circuit','rant') DB<2> x \%hash 0 HASH(0x3da37a8) 'a' => 1 'b' => 2 'blog' => 'rant' 'c' => 3 'log' => 'l' 'schema' => 's' 'schematic' => 'circuit' DB<3> x +{ %hash{grep !/^schema\|log$/, keys %hash } } # Note that t +he ^ only applies to schema, and the $ only applies to log, so it wil +l remove more than you might have meant 0 HASH(0x3f6e6f8) 'a' => 1 'b' => 2 'c' => 3 DB<4> x +{ %hash{grep !/^(schema\|log)$/, keys %hash } } # This vers +ion has all exclusions fully anchored 0 HASH(0x3f6ed10) 'a' => 1 'b' => 2 'blog' => 'rant' 'c' => 3 'schematic' => 'circuit' DB<5> $exclude1 = sub { my $href = shift; my $excl= join '\|', @_; +return +{ %$href{ grep !/^$excl$/, keys %$href } } } DB<6> $h_ref = \%hash DB<7> x $h_ref->$exclude1(qw/schema log/) 0 HASH(0x3f73640) 'a' => 1 'b' => 2 'c' => 3 DB<8> x $h_ref->$exclude1(qw/log schema/) 0 HASH(0x3f73988) 'a' => 1 'b' => 2 'blog' => 'rant' 'c' => 3 'schematic' => 'circuit' DB<9> $exclude2 = sub { my $href = shift; my $excl = join '\|', @_; r +eturn +{ %$href{ grep !/^($excl)$/, keys %$href } } } DB<10> x $h_ref->$exclude2(qw/schema log/) 0 HASH(0x3f73808) 'a' => 1 'b' => 2 'blog' => 'rant' 'c' => 3 'schematic' => 'circuit' [download]	[reply] [d/l] [select]
Re^4: Hash/Array slice : how to exclude items? -- be careful of anchoring by LanX (Saint) on Jan 24, 2023 at 18:02 UTC
Well spotted by you and badly tested by me, thanks. In the end the regex is a poor man's alternative for the unfortunately designed `smartmatch` operator `~~` Actually I was too occupied worrying if I need to `quotemeta` the input or if keeping the door open for regex-metas is a better interface, and forgot about precedence here. So another "fault" in the concept. =) Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply]


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