Data Types Master

Data Types in Perl

Paolo Marcatili - Programmazione 09-10

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Agenda

> Perl Basics> Hello World> Scalars> Arrays> Hashes


Task Today


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parsing

Parse a GO fileExtract gene names and function


Perl Basics


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PERL

Practical Extractionand Reporting Language

Handle text files Web (CGI) Small scripts

http://www.perltutorial.org/


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Install

Windowshttp://www.activestate.com/activeperl/Cygwin (linux emulation)

Linux / OS-XNative


Hello World!


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First script

Open an editor (e.g. gedit)

#!/usr/bin/perl -wuse strict;use warnings;print "Hello World!\n";

Save as -> first.pl


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How to run a script

Terminal -> move to the script folder

perl first.pl

orchmod a+x first.pl <- now it is executable by

everyone./first.pl <- ./ means ‘in this folder’


Scalars


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Scalars

my $scalar;$scalar=5;$scalar=$scalar+3;$scalar= “scalar vale $scalar\n”;print $scalar;

> scalar vale 8

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Scalars - 2

Scalar data can be number or string. In Perl, string and number can be used nearly interchangeable.

Scalar variable is used to hold scalar data. Scalar variable starts with dollar sign ($) followed by Perl identifier. Perl identifier can contain alphanumeric and underscores. It is not allowed to start with a digit.

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Examples #floating-point values my $x = 3.14; my $y = -2.78;

#integer values my $a = 1000; my $b = -2000;

my $s = "2000"; # similar to $s = 2000;

#strings my $str = "this is a string in Perl". my $str2 = 'this is also as string too'.

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Operations

my $x = 5 + 9; # Add 5 and 9, and then store the result in $x$x = 30 - 4; # Subtract 4 from 30 and then store the result in $x$x = 3 * 7; # Multiply 3 and 7 and then store the result in $x$x = 6 / 2; # Divide 6 by 2$x = 2 ** 8; # two to the power of 8$x = 3 % 2; # Remainder of 3 divided by 2$x++; # Increase $x by 1$x--; # Decrease $x by 1

my $y = $x; # Assign $x to $y$x += $y; # Add $y to $x$x -= $y; # Subtract $y from $x$x .= $y; # Append $y onto $x

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Operations - 2

my $x = 3;my $c = "he ";my $s = $c x $x; # $c repeated $x timesmy $b = "bye";print $s . "\n"; #print s and start a new line# similar toprint "$s\n";my $a = $s . $b; # Concatenate $s and $bprint $a;# Interpolationmy $x = 10;my $s = "you get $x";print $s;

Arrays


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boxed scalars

Scalar Array

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array - 1

("Perl","array","tutorial");(5,7,9,10);(5,7,9,"Perl","list");(1..20);();

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array - 2

my @str_array=("Perl","array","tutorial");my @num_array=(5,7,9,10);my @mixed_array=(5,7,9,"Perl","list");my @rg_array=(1..20);my @empty_array=();

print $str_array[1]; # 1st element is [0]

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operationsmy @int =(1,3,5,2);push(@int,10); #add 10 to @intprint "@int\n"; my $last = pop(@int); #remove 10 from @intprint "@int\n"; unshift(@int,0); #add 0 to @intprint "@int\n";my $start = shift(@int); # add 0 to @intprint "@int\n";

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on array

my @int =(1,3,5,2);

foreach my $element (@int){print “element is $element\n”;}

my @sorted=sort(@int);foreach my $element (@sorted){print “element is $element\n”;}

Hashes


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Hashes> Hashes are like array, they store collections of

scalars... but unlike arrays, indexing is by name (just like inreal life!!!)

> Two components to each hash entry:> Key example : name> Value example : phone number

> Hashes denoted with %> Example : %phoneDirectory

> Elements are accessed using {} (like [] in arrays)


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Hashes continued ...

> Adding a new key-value pair $phoneDirectory{“Shirly”} = 7267975

> Note the $ to specify “scalar” context!> Each key can have only one value

$phoneDirectory{“Shirly”} = 7265797 # overwrites previous assignment

> Multiple keys can have the same value

> Accessing the value of a key $phoneNumber =$phoneDirectory{“Shirly”};


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Hashes and Foreach> Foreach works in hashes as well!

foreach $person (keys (%phoneDirectory) ) {

print “$person: $phoneDirectory{$person}”;}

> Never depend on the order you put key/valuesin the hash! Perl has its own magic to makehashes amazingly fast!!


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Hashes and Sorting

> The sort function works with hashes as well> Sorting on the keys

foreach $person (sort keys %phoneDirectory) { print “$person : $directory{$person}\n”;}> This will print the phoneDirectory hash table in

alphabetical order based on the name of theperson, i.e. the key.


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Hash and Sorting cont...

> Sorting by value

foreach $person (sort {$phoneDirectory{$a} <=>$phoneDirectory{$b}} keys %phoneDirectory){

print “$person : $phoneDirectory{$person}\n”;

}

> Prints the person and their phone number in theorder of their respective phone numbers, i.e.the value.


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Exercise

> Chose your own test or use wget

> Identify the 10 most frequent words

> Sort the words alphabetically

> Sort the words by the number ofoccurrences


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Counting Words my %seen;

my $l=“Lorem ipsum”;my @w=split (“ “, $l);# questa è una funzione nuova…foreach my $word (@w){

$seen{$word}++;}print “Sorted by occurrences\n”;foreach my $word (sort {$seen{$a}<=>$seen{$b}} keys %seen){

print “Word $word N: $seen{$word}\n”;}

print “Sorted alphabetically\n”;foreach my $word (sort ( keys %seen)){print “Word $word N: $seen{$word}\n”;}


Data Types Master

Technology

print word

person keys

word n

person sort keys

word sort keys

foreach foreach

phonedirectory elements

phonedirectory hash