Debug a sort block

rpaskudniak has asked for the wisdom of the Perl Monks concerning the following question:

Perl revision 5 version 16 subversion 3

Greetings, oh Great Ones!

Here is a sort command that is barfing on me:

my @ptn_sortd = sort {    ${$partition_h{a}}{full_tabname}
                      cmp ${$partition_h{b}}{full_tabname}} @parnums;
[download]

This is greeted with a barrage of this error message:

Use of uninitialized value in string comparison (cmp) at ./<script nam
+e> line 156.
 at ./<script name> line 156.
Use of uninitialized value in string comparison (cmp) at ./<script nam
+e> line 156.
 at ./<script name>l line 156.
Use of uninitialized value in string comparison (cmp) at ./<script nam
+e> line 156.
 at ./<script name> line 156.
....
[download]

I have already proven that no item in the hash has an undefined {full_tabname} member. I used

  grep {defined(${$partition_h{$_}}{full_tabname}) }
[download]

to weed out the one such holdout. (That undefined name is separate mystery, out of scope for this question.) I have also confirmed that when I supply an actual value, the syntax does indeed return a string.

By the way, the hash keys are large-ish integers.

What could I possibly be doing wrong to deserve this frustrating punishment?

Thanks much for help here! -- RP

Comment on Debug a sort block Select or Download Code

Replies are listed 'Best First'.
Re: Debug a sort block by AnomalousMonk (Archbishop) on Jan 31, 2020 at 20:05 UTC
`${$partition_h{a}}{full_tabname}` Do you really mean `${$partition_h{a}}{full_tabname}` and not `${$partition_h{$a}}{full_tabname}` (`a` vice `$a`)? Update: It is possible (though usually very tedious) to put debug statements into a sort block as long as the comparison is the last expression evaluated: `c:\@Work\Perl\monks>perl -wMstrict -e "use Data::Dump qw(dd); ;; my @sorted = sort { dd $a, $b; $a cmp $b; } (qw(d a c e b), undef); dd \@sorted; " ("d", "a") ("c", "e") ("b", undef) Use of uninitialized value in string comparison (cmp) at -e line 1. ("a", "c") ("c", "d") ("d", "e") ("a", undef) Use of uninitialized value in string comparison (cmp) at -e line 1. ("a", "b") ("c", "b") [undef, "a", "b", "c", "d", "e"]` [download] (Update: Changed example code to use Data::Dump`::dd()` instead of print and to include an undef element in the list to be sorted.) Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^2: Debug a sort block by LanX (Saint) on Jan 31, 2020 at 21:41 UTC
> Update: It is possible (though usually very tedious) to put debug statements into a sort block In this case I'd rather replace the `sort` block with a function, it's match easier to set breakpoints and watch expressions then. `DB<1> sub by_num { return $a <=> $b } DB<2> x [sort by_num 1,11,2,12] 0 ARRAY(0x334b888) 0 1 1 2 2 11 3 12 DB<3>` [download] update added `return` to make mechanism obvious. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}	[reply] [d/l] [select]
Re: Debug a sort block by LanX (Saint) on Jan 31, 2020 at 21:22 UTC
It should be `$a` and `$b` not `a` and `b` ° On a side note: > `${$partition_h{$a}}{full_tabname}` your dereferencing syntax is kind of weird, the following is much easier to read and does the same: `$partition_h{$a}{full_tabname}` Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery FootballPerl is like chess, only without the dice} °) oh AnomalousMonk already told you! :)	[reply] [d/l] [select]
Re: Debug a sort block by karlgoethebier (Abbot) on Feb 01, 2020 at 14:37 UTC
Probably somehow related and interesting. Regards, Karl ŤThe Crux of the Biscuit is the Apostropheť `perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'`Help	[reply] [d/l]


P is for Practical
	PerlMonks

Debug a sort block

update