On Tue, Jul 8, 2014 at 9:31 PM, Assaf Gordon <[email protected]> wrote:
> Hello,
>
> Few Perl questions if you please, regarding the optimal (Perlish) way to
> do things.
> One constraint though: my code needs to run on old Perls (5.8 and up),
> and can only use standard modules (so it doesn't help me if there's a CPAN
> module which does exactly what I need - I can't require the users to
> install it).
>
> 1. How to emulate Python's enumerate() function ?
>
> Given a list, how to make a list of tuples with indexes/values ?
>
> The non-perl way:
> my @list = ('A'..'Z');
> my @output;
> for (my @i = 0; $i < $#list ; ++$i) {
> push @output, [ $i, $list[$i] ];
> }
>
> Perl way?
> my @output = map { [ $i, $list[$i] ] } ( 0 .. $#list ) ;
>
> Is there a cleaner way (I can't use List::MoreUtils::pairwise sadly).
>
There's nothing wrong with your solution. Your code does what you want, and
fits the requirements you gave (it doesn't use a different module). What
don't you like about it?
>
>
> 2. Given a hash with string-keys and numeric-values, how to return a list
> of the keys,
> sorted by the values?
> e.g
> my %h = ( "hello" => 4,
> "world" => 1,
> "foo" => 2,
> "bar" => 3 )
> return:
> ( "world", "foo", "bar", "hello" )
>
> I came up with:
> my @result =
> map { $_->[0] }
> sort { $a->[1] <=> $b->[1] }
> map { [ $_, $h{$_} ] }
> keys %h;
>
> Is there a better way?
>
This is fine.
>
>
> 3. How to automatically use the appropriate "cmp" or "<=>" ?
> I have a function that accepts a list.
> The list is either all strings, or all numbers.
> Half-way through, the function needs to sort the list.
> Is there a simple way to know whether to use "cmp" or "<=>" ?
>
> I don't want to duplicate code with two functions, and would prefer to
> avoid adding an extra parameter to the function telling it if these are
> numbers or strings.
>
sub untested_solution {
my @input = @_;
return if @input == 0;
# We were promised the input is at least consistent, so sniff the first
element.
my $cmp = looks_like_a_number($input[0]) ?
sub { $a <=> $b } : sub { $a cmp $b };
return sort $cmp, @input;
}
# You could find a better implementation of this. Probably mucking around
the C API
# there's even a "correct" (more or less) way, but it sounds like you can't
use modules.
sub looks_like_a_number {
my ($x) = @_;
no warnings;
return $x eq $x+0;
}
>
> Thanks,
> -Assaf
>
>
>
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