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Re: Converting some MapReduce PHP scripts to Perl

by Tanktalus (Canon)
on Aug 12, 2011 at 22:30 UTC ( #920097=note: print w/ replies, xml ) Need Help??


in reply to Converting some MapReduce PHP scripts to Perl

The json_decode in PHP there looks like the same thing as decode_json in the JSON (or JSON::XS) module in perl. Note, however, that PHP is kinda lying to you - key-value pairs are stored in maps or, in perl, hashes. That PHP doesn't differentiate may make PHP easier, but makes translating what you've learned in PHP to other languages harder. (To be fair, translating from Perl to, say, C++, isn't trivial, either, for similar abstraction-based reasons.)

Presumably, that get_object_vars function exists elsewhere in the code, though your printouts make it look like it doesn't do anything, as $value1 already will have that value by way of the decode_json function. So, a rough copy would be:

#!/usr/bin/perl use JSON; my %data; while (<DATA>) { my ($key, $value) = split ' ', $_; $value = decode_json($value); if (exists $data{$key}) { while (my ($k,$v) = each %{$value[1]}) { $data{$key}{$k} += $v; } } else { $data{$key} = $value; } } use Data::Dumper qw(Dumper); print Dumper(\%data); __END__ 36dc0d7d0ac25ce60898c36ca135fbbd [[12051,840,501,33],{"23602":22}] 4c38528ffe96a15c90e8cfcaaad048e3 [[13308,124,-1,62],{"8002":12}] 5557a6bed3793133754d288e2b58763a [[2197,840,751,6],{"16501":1}] 5a9c1f69434c1a8b1d7880ef03ae4264 [[7525,616,-1,14347],{"24902":37}] 87f63173118df680a4c1d63b7953faf3 [[2765,458,-1,11937],{"3102":15}] 901d1a5dbd4ed87fd68db2513fb29762 [[1828,124,-1,63],{"8002":379}] c23a2b2c10af8af96b1b24ddd4cc53d4 [[62,840,820,38],{"16801":303}] d7af9cd8573ecbec6d42e453439e3e0f [[4680,124,-1,63],{"1012":1896}] d93adab6b345608d38ea84811012dce8 [[114,840,819,48],{"22502":322,"80 +02":3}] ffd50dd8b4986f40634d6b5925dc04c6 [[6089,840,803,5],{"1252":1}]
Not sure if that's entirely correct, but it seems to work.


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Re^2: Converting some MapReduce PHP scripts to Perl
by fullermd (Curate) on Aug 12, 2011 at 23:30 UTC
    Presumably, that get_object_vars function exists elsewhere in the code

    Actually, it's a standard PHP function. It turns an object into an (associative) array of its properties.

    PHP's json_decode turns the map/hash/whatever into technically an object rather than an array. Little odd, though perhaps fitting the 'JS' part of 'JSON' in a way. In that case, the extra step is needed to get something you can refer to as an array. From the print_r() output, it looks like it may have actually turned it into an array since it only had numeric keys, but that's too deep in PHP's DWIM for me to suss out.

Re^2: Converting some MapReduce PHP scripts to Perl
by regan99 (Initiate) on Aug 13, 2011 at 00:39 UTC

    DISREGARD BELOW!!! I figured it out... I forgot to use encode_json on $data{$key} to properly format the output. Thanks for the help and suggestions!

    That works! Thank you for the reply. The only issue I am having now is with the output. I'm trying to get the output to be in the form:

    $key . "\t"' . $data{$key} . "\n";

    But when I iterate through the %data hash, the key and the tab come out as expected, but the value comes out as an array reference. I've tried to dereference it with no success. The dumper output for one key->value pair of the %data hash shows this:

    '5557a6bed3793133754d288e2b58763a' => [ [ 2197, 840, 751, 6 ], { '16501' => 1 } ]

    This looks as though the value contains both an array and a hash. Is there a way I can dereference those so that my output prints those values out as a string rather than the reference? For example, I currently get this:

    5557a6bed3793133754d288e2b58763a ARRAY(0x441c780)

    When what I'm after is this:

    5557a6bed3793133754d288e2b58763a [[2197,840,751,6],{"16501":1}]

    ...and here's the code I'm using to output the pairs:

    foreach $key (keys %data) { print $key . "\t" . "$data{$key}" . "\n"; }

    Any ideas how to dereference that $data{key} to get the string instead of the array reference?

      As you mentioned, the data contains an array and a hash, it needs more than just a print ... I'm sure there are many ways to do it but here is what i have ...
      foreach my $key ( keys %data ) { my $out = ''; foreach my $s ( @{ $data{$key}} ) { if ( ref $s eq 'ARRAY' ) { $out .= '[' . ( join ',', @$s ) . ']'; } else { while ( my ($k,$v) = each %$s ) { $out .= ",{\"$k\":$v}"; } } } print $key . "\t[$out]\n"; }

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