Finding hash keys in array

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

Hi Monks!
I am trying to find if some array elements are in a hash key, to build a table alternating the text in the TDs if the name in the array match any hash key, here is a sample of what I am trying to do:

my @arr_of_names = qw(Mary John Ann);
my $txt;

my $table = qq|<table>|;

 foreach my $key ( sort(keys %$all_names )) {
   
   foreach my $name ( @arr_of_names ) {

     if($name eq $key) {
     
       $txt = "BAD";
       $table = $table. qq|<tr><td>$txt - $key</td></tr>";
       
     }else{

       $txt = "GOOD";
       $table = $table. qq|<tr><td>$txt - $key</td></tr>";
    }
                             
 }

 $table = $table. qq|</table>|;
 
 print $table;
[download]

Thanks, I hope I was clear in my question.

Comment on Finding hash keys in array Download Code

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Re: Finding hash keys in array by Grimy (Pilgrim) on May 29, 2013 at 18:42 UTC
Looping through all the keys in the hash is very inefficient. To check if $name is a key of %$all_names, you could use : `exists $$all_names{$name}; %$all_names ~~ $name; # Shortcut using the smartmatch operator` [download] Note that this isn't the same as `defined $$all_names{$names}`. If you do `$$all_names{$key} = undef`, `exists` would return true (because the key exists), but `defined` would return false (because the value is undefined). To select elements from an array based on a condition, you can use `grep { condition } @array`. Putting it all together, to get all elements of @arr_of_names that are keys of %$all_names, you can try this : `@good = grep { %$all_names ~~ $_ } @arr_of_names;` [download] Note that inside the `grep` condition, the element being tested is aliased to $_.	[reply] [d/l] [select]
Re: Finding hash keys in array by kcott (Archbishop) on May 30, 2013 at 05:15 UTC
Problems I found with your code: Your design looks wrong: you'll be creating a table row for every key in `%$all_names` for every element in `@arr_of_names`. Reading through the entire `@arr_of_names` for every key in `%$all_names` is unecessary and inefficient. Assigning to `$txt` for every key in `%$all_names` for every element in `@arr_of_names` is unecessary and inefficient. Concatenating text to `$table` for every key in `%$all_names` for every element in `@arr_of_names` is unecessary and inefficient. You don't declare the hashref `$all_names` or show its data. Here's how I might have tackled this type of problem: `$ perl -Mstrict -Mwarnings -le ' my @all_names = qw{Mary Ken John Ann}; my @good_names = qw{Mary John Ann}; my %all_name_data = map { $_ => 1 } @all_names; my %is_good_name = map { $_ => 1 } @good_names; print "<table>"; for (sort keys %all_name_data) { print "\t<tr><td>", $is_good_name{$_} ? "GOOD" : "BAD", " - $_</td></tr>"; } print "</table>"; ' <table> <tr><td>GOOD - Ann</td></tr> <tr><td>GOOD - John</td></tr> <tr><td>BAD - Ken</td></tr> <tr><td>GOOD - Mary</td></tr> </table>` [download] -- Ken	[reply] [d/l] [select]
Re: Finding hash keys in array by LanX (Saint) on May 29, 2013 at 18:01 UTC
> Thanks, I hope I was clear in my question. Which question? There is even not a single questionmark in your post. Cheers Rolf ( addicted to the Perl Programming Language)	[reply]