Bad index while coercing array into hash in Perl

Question

Below is the code

my $results = $session->array_of_hash_for_cursor("check_if_receipts_exist", 0, @params);
next if( scalar @{$results} <= 0 );
$logger->info("Retrieved number of records: ".scalar @$results);
foreach my $row( sort { $results->{$b}->{epoch_received_date} cmp $results->{$a}->{epoch_received_date} } keys %{$results} )
      {
       //logic
      }

'check_if_receipts_exists' is a SQL query which returns some results. Which I try to execute this, I am getting the following error, Bad index while coercing array into hash

I am new to Perl. Can someone please point out the mistake I am making?

Where is $session coming from?

Wooble
– Wooble

2012-01-13 17:31:52 +00:00
Commented Jan 13, 2012 at 17:31 — Wooble
– Wooble, Commented Jan 13, 2012 at 17:31

ikegami · Accepted Answer · 2012-01-13 18:45:15Z

3

Is $results a hash reference or an array reference?

In some places you are using it like an array reference:

scalar @{$results}

and in other places you are using it like a hash reference:

$results->{$b}->{...}
keys %{$results}

It can't be both (at least not without some heavy overload magic).

If I can infer from the name of the function that sets $results, it should be a reference to a list of hash references, then a few tweaks will set it right:

Using @{$results} is correct; this expression is "an array of hash references"
The last argument to sort should be a list, but the correct list to pass is @{$results}, not keys %{$results}.
Then the parameters $a and $b inside the sort function will be members of @{$results}, that is, they will be hash references. So the comparison to make is

$a->{epoch_received_date} cmp $b->{epoch_retrieve_data}

and not

    $results->{$a}->{...} cmp $results->{$b}->{...}

All together:

my $results = $session->array_of_hash_for_cursor(
   "check_if_receipts_exist", 0, @params);
next if !@$results;
$logger->info("Retrieved number of records: ".@$results);
for my $row (
    sort {
        $b->{epoch_received_date}
          cmp
        $a->{epoch_received_date}
    } @$results
) {
   # logic
}

edited Jan 13, 2012 at 18:45

ikegami

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answered Jan 13, 2012 at 17:36

mob

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5 Comments

carkct Over a year ago

After making the above changes, I am getting the following error, Type of arg 1 to keys must be hash (not array dereference) at ...

mob Over a year ago

@carkct - Read the suggestions again. I doubt there is any need to use keys. I'm guessing you should be using sort {...} @{$results}.

mob Over a year ago

And keep your chin up. This stuff is complicated and confusing, but once you get the hang of it, it is very powerful and expressive.

carkct Over a year ago

I tried using foreach my $row( sort { {$b}->{epoch_received_date} cmp {$a}->{epoch_received_date} } @{$results} ) and it worked. Thanks.

bvr Over a year ago

@ikegami - I think there is an error in summary code (next if @$results seems reverse logic to OP's code)

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