PERL Beginners - Moving between hashes 2.

Author

Moving between hashes 2.

Michael Robeson

2004-09-24, 3:59 pm

Gunnar,

Thanks so much for the help and the links! They help quit a bit. I
decided to use the if statement you posted:

if ( $aa eq '-' ) {
$hash3{$_} .= '---';
} else {
$hash3{$_} .= substr $dna,0,3,'';
}

instead of:

$hash3{$_} .= $aa eq '-' ? '---' : substr $dna,0,3,'';

only because I had to add a $count++ function within the else statement
(shown below) to accomplish another task within my larger script:

if ( $aa eq '-' ) {
$hash3{$_} .= '---';
} else {
$hash3{$_} .= substr $dna,0,3,'';
$count++
}

I couldn't figure out if it was possible to add $count++ within the ?:
statement above. I tried but could not get it to work.

However, everything works well at this point. Again, I really
appreciate the help!

-Mike

On Sep 20, 2004, at 6:55 PM, beginners-digest-help@perl.org wrote:

> From: Gunnar Hjalmarsson <noreply@gunnar.cc>
> Date: September 19, 2004 9:12:32 PM MDT
> To: beginners@perl.org
> Subject: Re: Moving between hashes 2.
>
>
> Michael S. Robeson II wrote:
>
> Well, before an attempt to explain and/or point you to the applicable
> docs, I'd like to change my mind once again. :) This is my latest
> idea:
>
> my %hash3;
> for ( keys %hash1 ) {
> my $dna = $hash2{$_};
> for my $aa ( split //, $hash1{$_} ) {
> $hash3{$_} .= $aa eq '-' ? '---' : substr $dna,0,3,'';
> }
> }
>
> I'll assume that you don't have a problem with the outer loop, that
> simply iterates over the hash keys. As a first step in each iteration
> I copy the DNA sequence to the $dna variable, so as to not destroying
> %hash2.
>
> Over to the 'tricky' part. The inner loop iterates over each character
> in the amino-acid sequence data, and respective character is assigned
> to $aa. For that I use the split() function:
> http://www.perldoc.com/perl5.8.4/pod/func/split.html
>
>
> That sounds strange to me, because that's how it should be used...
> Read about the conditional operator in
> http://www.perldoc.com/perl5.8.4/pod/perlop.html
>
> OTOH, that notation is basically the same as:
>
> if ( $aa eq '-' ) {
> $hash3{$_} .= '---';
> } else {
> $hash3{$_} .= substr $dna,0,3,'';
> }
>
> which is a little more intuitive (at least I think it is).
>
>
> Precisely.
>
>
> Hopefully the if/else statement makes it easier to grasp, and the '.='
> operator is used just for appending something to a string.
>
> Finally we have my use of the substr() function.
> http://www.perldoc.com/perl5.8.4/pod/func/substr.html
> It returns the first three characters in $dna, and since I also pass
> the null string as the fourth argument, it changes the content of $dna
> at the same time, i.e. it replaces the first three characters with
> nothing.
>
> HTH. If you need further explanations, you'll have to ask specific
> questions.
>
> --
> Gunnar Hjalmarsson
> Email: http://www.gunnar.cc/cgi-bin/contact.pl
>
>

Gunnar Hjalmarsson

2004-09-24, 3:59 pm

Michael Robeson wrote:
> I decided to use the if statement you posted:

<snip>

> only because I had to add a $count++ function within the else
> statement (shown below) to accomplish another task within my larger
> script:
>
> if ( $aa eq '-' ) {
> $hash3{$_} .= '---';
> } else {
> $hash3{$_} .= substr $dna,0,3,'';
> $count++
> }
>
> I couldn't figure out if it was possible to add $count++ within the
> ?: statement above. I tried but could not get it to work.

Right, the conditional operator is merely designed for assignment.

OTOH, you don't need a loop to count a certain type of characters in a
string:

my $string = 'mfg--f';
my $count = $string =~ tr/a-z//;

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

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