I need to clean json data from nulls, empty arrays, empty hashes. Current solution: 

 

#!/usr/bin/perl -CSDA

# Removes empty arrays, empty objects, and nulls from json structure. 

use utf8; 
use Modern::Perl qw{2017}; 
use JSON; 
use Data::Dumper; 

sub tidyup_json { 
    my ($r) = @_; 

    if (ref $r eq "HASH") { 
        for my $k (keys %$r) { 
            tidyup_json($$r{$k}); 
            delete $$r{$k} if 
                (ref $$r{$k} eq "HASH" && ! %{$$r{$k}}) or
                (ref $$r{$k} eq "ARRAY" && ! @{$$r{$k}}) or
                ! defined $$r{$k}; 
        }

    } elsif (ref $r eq "ARRAY") { 
        tidyup_json($$r[$_]) for 0 .. @$r - 1; 
        @$r = grep { not ( 
            (ref $_ eq "HASH" && ! %$_) or
            (ref $_ eq "ARRAY" && ! @$_) or
            ! defined $_
        ) } @$r; 
    } 

    # use "$_[0]", because "$_[0]" is an alias to real reference that 
+was passed to the function 
    $_[0] = undef if 
        (ref $r eq "HASH" && ! %$r) or
        (ref $r eq "ARRAY" && ! @$r); 
}

my $json = JSON->new->allow_nonref->relaxed->decode(do { local $/; <ST
+DIN>; }); 
tidyup_json($json); 

print JSON->new->pretty->allow_nonref->canonical->encode($json);

[download]

What's the problem? See the "$_[0]" at the end of function? This is an alias for passed reference of json data. If that json data is empty hash, then the data must become "undef". So I have to modify data outside of function -- using alias. Is there more elegant way to handle it?

Here are results: 
 


# echo '{"empty inner hash": {}, "empty inner array": [], "some undef"
+: null }' | ./tidyup_json 
null


# echo '{"empty inner hash": {}, "empty inner array": [1], "some undef
+": null }' | ./tidyup_json 
{
   "empty inner array" : [
      1
   ]
}


# echo '{"empty inner hash": {}, "empty inner array": [1], "some undef
+": 7 }' | ./tidyup_json 
{
   "empty inner array" : [
      1
   ],
   "some undef" : 7
}

# echo '{ }' | ./tidyup_json    ## !!! important to return null 
null

[download]

PS. Beware that "true" and "false" jsonish data are references to blessed hashes.

In reply to Tidy up json from nulls, empty arrays and hashes by leszekdubiel

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