This document provides an overview of data types in Perl, including scalars, arrays, and hashes. Scalars can hold single numeric or string values and are denoted with a dollar sign. Arrays hold collections of scalar values and are denoted with an at sign. Hashes store key-value pairs and are denoted with a percent sign. The document provides examples of declaring and accessing each data type, and describes common operations like sorting, iterating with foreach loops, and adding/removing elements from arrays.

1. Data Types in Perl
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2. Agenda
> Perl Basics
> Hello World
> Scalars
> Arrays
> Hashes
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3. Task Today
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4. parsing
Parse a GO file
Extract gene names and function
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5. Perl Basics
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6. PERL
Practical Extraction
and Reporting Language
 Handle text files
 Web (CGI)
 Small scripts
http://www.perltutorial.org/
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7. Install
Windows
http://www.activestate.com/activeperl/
Cygwin (linux emulation)
Linux / OS-X
Native
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8. Hello World!
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9. First script
Open an editor (e.g. gedit)
#!/usr/bin/perl -w
use strict;
use warnings;
print "Hello World!n";
Save as -> first.pl
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10. How to run a script
Terminal -> move to the script folder
perl first.pl
or
chmod a+x first.pl <- now it is executable by
everyone
./first.pl <- ./ means ‘in this folder’
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11. Scalars
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12. Scalars
my $scalar;
$scalar=5;
$scalar=$scalar+3;
$scalar= “scalar vale $scalarn”;
print $scalar;
> scalar vale 8
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13. Scalars - 2
 Scalar data can be number or string.
 In Perl, string and number can be used
nearly interchangeable.
 Scalar variable is used to hold scalar data.
 Scalar variable starts with dollar sign ($)
followed by Perl identifier.
 Perl identifier can contain
alphanumeric and underscores.
 It is not allowed to start with a digit.
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14. 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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15. 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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16. Operations - 2
my $x = 3;
my $c = "he ";
my $s = $c x $x; # $c repeated $x times
my $b = "bye";
print $s . "n"; #print s and start a new line
# similar to
print "$sn";
my $a = $s . $b; # Concatenate $s and $b
print $a;
# Interpolation
my $x = 10;
my $s = "you get $x";
print $s;
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17. Arrays
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18. boxed scalars
Scalar Array
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19. array - 1
("Perl","array","tutorial");
(5,7,9,10);
(5,7,9,"Perl","list");
(1..20);
();
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20. 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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21. operations
my @int =(1,3,5,2);
push(@int,10); #add 10 to @int
print "@intn";
my $last = pop(@int); #remove 10 from @int
print "@intn";
unshift(@int,0); #add 0 to @int
print "@intn";
my $start = shift(@int); # add 0 to @int
print "@intn";
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22. on array
my @int =(1,3,5,2);
foreach my $element (@int){
print “element is $elementn”;
}
my @sorted=sort(@int);
foreach my $element (@sorted){
print “element is $elementn”;
}
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23. Hashes
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24. Hashes
> Hashes are like array, they store collections of
scalars
... but unlike arrays, indexing is by name (just like in
real 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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25. 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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26. 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/values
in the hash! Perl has its own magic to make
hashes amazingly fast!!
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27. 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 the
person, i.e. the key.
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28. 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 the
order of their respective phone numbers, i.e.
the value.
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29. Exercise
> Chose your own test or use wget
> Identify the 10 most frequent words
> Sort the words alphabetically
> Sort the words by the number of
occurrences
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30. 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 occurrencesn”;
foreach my $word (sort {$seen{$a}<=>$seen{$b}} keys %seen){
print “Word $word N: $seen{$word}n”;
}
print “Sorted alphabeticallyn”;
foreach my $word (sort ( keys %seen)){
print “Word $word N: $seen{$word}n”;
}
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