Re: How to Check Hashes for Missing Items when Keys can be Values and vice versa

[ozboomer]

Many thanks, everyone, for the useful responses.

I've had a bit of a go with some of the suggestions... and I have something that does what I need (I think - more testing required, as usual). The updated sample code follows:-

# Ref: http://www.perlmonks.com/?node_id=1196078

use Data::Dumper;

%data_hash   = ();
%output_hash = ();

@master_dsks  = ( 70, 71, 75, 90, 91, 92, 93, 96, 97, 
                  98, 99, 190, 204, 205, 550, 551 );   
                
@master_sites  = ( 350, 377, 510, 512, 580, 587, 
                   590, 1100, 1105, 1107, 1108 );

# ----
                   
printf("All Known Dsks:\n");       # Show ALL the known dsks
foreach (@master_dsks) {
   printf("%s ", $_);
}
printf("\n\n");

# ----
                   
printf("All Known Sites:\n");      # Show ALL the known sites
foreach (@master_sites) {
   printf("%s ", $_);
}
printf("\n\n");

# ----
                   
while( <DATA> ) {                          # Build list of unique (sit
+e:dsk) items
   ($site, $buf) = split(/,/, $_);

   @input_item = split(/:/, $buf);
   foreach $input_field (@input_item) {    # EX: "VAR8=36!206!207!"
      @dsk_list = ($input_field =~ /([0-9]+)!([0-9]+)!$/);  # Get last
+ 2 of 3 items
      
      foreach $dsk (@dsk_list) {           # Each dsk item in the inpu
+t...
         next if ($dsk == 0);              # Skip '0' dsk items
         $key = $site . ":" . $dsk;        # Build composite key
         $data_hash{$key}++;               # ...and save it
      }
   }
}

foreach $key ( sort keys %data_hash ) {    # Build list of dsk -> (mul
+ti sites)
   ($site, $dsk) = split(/:/, $key);
   
   push( @{ $output_hash{$dsk} }, $site ); # ... dsk -> (multi sites)
   push( @{ $site_2_dsk{$site} }, $dsk );  # !!! ADDITION !!! ... site
+ -> (multi dsks)
}

# ----

printf("List of sites for each used dsk:\n");
foreach $dsk (sort {$a <=> $b} keys %output_hash) {  # Show list of si
+tes for each dsk
   printf("Dsk: %d: ... ", $dsk);
   foreach $site (sort {$a <=> $b} @{$output_hash{$dsk}}) {
      printf("  %d ", $site);
   }
   printf("\n");
}
printf("\n");

printf("List of dsks for each used site:\n");
foreach $site (sort {$a <=> $b} keys %site_2_dsk) {  # Show list of ds
+ks for each site
   printf("Site: %d: ... ", $site);
   foreach $dsk (sort {$a <=> $b} @{$site_2_dsk{$site}}) {
      printf("  %d ", $dsk);
   }
   printf("\n");
}
printf("\n");

# ----

my %master_dsks_hash = map { $_ , "" } @master_dsks;   # Hash of ALL d
+sks
delete @master_dsks_hash{keys %output_hash};           # Delete the US
+ED dsks
@unused_dsks = (keys %master_dsks_hash);               # ...leaving th
+e UNUSED dsks

printf("Dsks that are known but unused:\n");
foreach (sort {$a<=>$b} @unused_dsks) {
   printf("%s ", $_);
}
printf("\n\n");

# ----

my %master_sites_hash = map { $_ , "" } @master_sites; # Hash of ALL s
+ites
delete @master_sites_hash{keys %site_2_dsk};           # Delete the US
+ED sites
@unused_sites = (keys %master_sites_hash);             # ...leaving th
+e UNUSED sites

printf("Sites that are known but unused:\n");
foreach (sort {$a<=>$b} @unused_sites) {
   printf("%s ", $_);
}
printf("\n\n");

__DATA__
1108,VAR6=36!204!205!:VAR8=36!206!207!:VAR13=36!70!0!:VAR14=36!70!71!:
+VAR15=36!71!0!
377,VAR12=36!97!96!
512,VAR6=36!90!91!:VAR8=36!92!93!:VAR11=36!0!70!:VAR12=36!189!190!
587,VAR2=36!550!0!:VAR4=36!554!0!:VAR6=36!551!0!

....and the output:-

All Known Dsks:
70 71 75 90 91 92 93 96 97 98 99 190 204 205 550 551 

All Known Sites:
350 377 510 512 580 587 590 1100 1105 1107 1108 

List of sites for each used dsk:
Dsk: 70: ...   512   1108 
Dsk: 71: ...   1108 
Dsk: 90: ...   512 
Dsk: 91: ...   512 
Dsk: 92: ...   512 
Dsk: 93: ...   512 
Dsk: 96: ...   377 
Dsk: 97: ...   377 
Dsk: 189: ...   512 
Dsk: 190: ...   512 
Dsk: 204: ...   1108 
Dsk: 205: ...   1108 
Dsk: 206: ...   1108 
Dsk: 207: ...   1108 
Dsk: 550: ...   587 
Dsk: 551: ...   587 
Dsk: 554: ...   587 

List of dsks for each used site:
Site: 377: ...   96   97 
Site: 512: ...   70   90   91   92   93   189   190 
Site: 587: ...   550   551   554 
Site: 1108: ...   70   71   204   205   206   207 

Dsks that are known but unused:
75 98 99 

Sites that are known but unused:
350 510 580 590 1100 1105 1107

BTW.. Not using the 'warnings' and 'strict' pragmas is fair enough comment.. but this is isolated, sample code... so I'm not too fussed about using them in this context.

Similarly, as I've been cutting code since the 1970s or something, I tend to pre-declare constants, variables, etc at the top of a block or module and then I know where to find all the initializations and comments about the identifiers I use in the code... instead of trying to find the 'first instance' (the 'my' declaration) of an identifier's use in some part of a mass of code when debugging/trying to understand some code - 'tis just easier for me.

..and Re: the issue of 'exists' ... trying to understand the perldoc description gives me too much of a headache:-

A hash or array element can be true only if it's defined and defined only if it exists, but the reverse doesn't necessarily hold true.

...but I take the point.

Thanks again for the most useful posts.

[choroba]

> I know where to find all the initializations and comments about the identifiers

With good variable names, no comments are needed. And there shouldn't be a block larger than one screen, so you don't have to scroll to find the initialization. See Skimmable Code by schwern.

[BillKSmith]

I agree that you habit of pre-declaring variables largely defeats the advantage of using strict (although it is still useful in detecting misspelled variables). Your suggestion of defining them at "first instance" is not much better. If fact, it can introduce errors (which strict can detect). A better strategy is to declare all variables in the "smallest possible scope". This does require some effort in writing new code and it does little to help your reader find the declarations. The advantage to you is that it greatly reduces the possibility of misusing a variable. The advantage to your reader is that, when he comes to the end of the scope, he knows for certain that he has seen all the references to the variable.

[pryrt]

trying to understand the perldoc description givees me too much of a headache:-

A hash or array element can be true only if it's defined and defined only if it exists, but the reverse doesn't necessarily hold true.

here's a Venn(ish) diagram in beautiful ASCII art that may or may not help, with examples on the side

universe of possible hash elements in Perl
+--------------------------------------+
| elements that exist                  |            $hash{element_exis
+ts};                  # this example: exists, undefined, false
|  +--------------------------------+  |
|  | elements that are defined      |  |            $hash{element_defi
+ned} = function_def();# this example: exists, defined, unknown false/
+true
|  |  +--------------------------+  |  |
|  |  |  elements that are true  |  |  |            $hash{element_true
+} = 1;                # this example: exists, defined, true
|  |  +--------------------------+  |  |
|  |                                |  |
|  |  +--------------------------+  |  |
|  |  : elements that are false  :  |  |            $hash{element_fals
+e} = function_false();# this example: exists, defined, false
|  |  :  +-------------------+   :  |  |
|  |  :  | false but defined |   :  |  |            $hash{element_fals
+e_defined} = 0;       # this example: exists, defined, false
|  |  :  +-------------------+   :  |  |
|  +--:--------------------------:--+  |
|     :                          :     |
|  +--:--------------------------:--+  |
|  |  :  +-------------------+   :  |  |
|  |  :  | false but undef   |   :  |  |            $hash{element_fals
+e_undefined} = undef; # this example: exists, undefined, false
|  |  :  +-------------------+   :  |  |
|  |  +--------------------------+  |  |
|  | elements that are undefined    |  |            $hash{element_unde
+fined};               # this example: exists, undefined, false
|  +--------------------------------+  |
+--------------------------------------+

Note that the ASCII art combined with wanting space for labels sometimes implies there is room in the Perl universe for combinations that aren't actually possible: for example, there are no elements that are undefined but not false, because perl coerces undefined to false.