Re^3: reduce like iterators

Oops, adjusted:

my @b = @{ reduce { push @$a, $b if !@$a || $b ne $a->[-1]; $a } [], @
+a };
[download]

If one were to make a list version of reduce, the callback would need access to three variables: The list (say $_), the state (say $a), the current value (say $b). The problem could be solved as follows:

my @b = list_reduce { push @$_, $b if !@$_ || $b ne $_->[-1]; undef } 
+undef, @a;

my @b = list_reduce { push @$_, $b if $a || $b ne $_->[-1]; 0 } 1, @a;

my @b = list_reduce { push @$_, $b if defined($b) && $b ne $a; $b } un
+def, @a;

my @b = list_reduce { push @$_, grep defined && $_ ne $a, $b; $b } und
+ef, @a;
[download]

(@a may not start with undef for the last two to work properly.)

Update: Added everything after the first block of code.

Comment on Re^3: reduce like iterators Select or Download Code

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Re^4: reduce like iterators by Anonymous Monk on Jan 09, 2024 at 08:28 UTC
`my @b = @{ reduce { push @$a, $b if !@$a \|\| $b ne $a->[-1]; $a } [], @ +a };` [download] This is really clever and should be included in List::Util: https://rt.cpan.org/Ticket/Display.html?id=150773. Note I had to disambiguate reduce by adding a '+'.	[reply] [d/l]
Re^5: reduce like iterators by jdporter (Paladin) on Jan 09, 2024 at 14:05 UTC
I had to disambiguate reduce by adding a '+'. Did you?	[reply]
Re^6: reduce like iterators by kcott (Archbishop) on Jan 09, 2024 at 14:50 UTC
"Did you?" I did. Syntax error without "+": `$ perl -MO=Deparse -e 'my @b = @{ reduce { push @$a, $b if !@$a \|\| $b +ne $a->[-1]; $a } [], @a };' syntax error at -e line 1, near "$b if" -e had compilation errors.` [download] Syntax OK with "+": `$ perl -MO=Deparse -e 'my @b = @{ +reduce { push @$a, $b if !@$a \|\| $b + ne $a->[-1]; $a } [], @a };' my(@b) = @{do { push @$a, $b if not @$a or $b ne $a->[-1]; $a }->reduce([], @a);}; -e syntax OK` [download] — Ken	[reply] [d/l] [select]
Re^7: reduce like iterators by ikegami (Patriarch) on Jan 10, 2024 at 15:45 UTC
Re^7: reduce like iterators by jdporter (Paladin) on Jan 09, 2024 at 16:27 UTC
Re^8: reduce like iterators by kcott (Archbishop) on Jan 10, 2024 at 01:01 UTC
Some notes below your chosen depth have not been shown here
Re^4: reduce like iterators by LanX (Saint) on Jan 03, 2011 at 19:13 UTC
> > `my @b = @{ reduce { push @$a, $b if @$a && $b ne $a->[-1]; $a } [], @a };` And I said: > (Sure I could use $a as an array-ref for accumulation, not very elegant...) Cheers Rolf	[reply] [d/l]
Re^5: reduce like iterators by ikegami (Patriarch) on Jan 03, 2011 at 19:18 UTC
But as I've shown in the update, it's not very elegant if you don't either.	[reply]
Re^6: reduce like iterators by ikegami (Patriarch) on Jan 03, 2011 at 19:28 UTC
It's a bit cleaner if ($state, @to_push) is returned. `my @b = list_reduce { undef, !@$_ \|\| $b ne $_->[-1] ? $b : () } undef, + @a; my @b = list_reduce { 0, !@$_ \|\| $b ne $_->[-1] ? $b : () } 1, @a; my @b = list_reduce { $b, defined($b) && $b ne $a ? $b : () } undef, @ +a; my @b = list_reduce { $b, grep defined && $_ ne $a, $b } undef, @a;` [download] (`@a` may not start with undef for the last two to work properly.) This actually looks like `map` now (as it should).	[reply] [d/l] [select]


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