hashes (associative arrays)
DESCRIPTION
Hashes (associative arrays). Hash Motivation. Let's say we want to create a phone book . . . Enter a name that will be added to the phone book: Dudi Enter a phone number: 6409245 Enter a name that will be added to the phone book: Dudu Enter a phone number: 6407693. %hash. =>. "a". 5. - PowerPoint PPT PresentationTRANSCRIPT
8.1
Hashes(associative arrays)
8.2
Let's say we want to create a phone book . . .
Enter a name that will be added to the phone book:
Dudi
Enter a phone number:
6409245
Enter a name that will be added to the phone book:
Dudu
Enter a phone number:
6407693
Hash Motivation
8.3
An associative array (or simply – a hash) is an unordered set of
pairs of keys and values. Each key is associated with a value.
A hash variable name always start with a “%”:
my %hash;
Initialization:
%hash = ("a"=>5, "bob"=>"zzz", 50=>"John");
Accessing:
you can access a value by its key:
print $hash{50}; John
Tip you can reset the hash (to an empty one) by %hash = ();
Hash – an associative array
%hash
5"a" >=
"zzz""bob" >=
"John"50 >=
8.4
modifying :
$hash{bob} = "aaa"; (modifying an existing value)
adding :
$hash{555} = "z"; (adding a new key-value pair)
You can ask whether a certain key exists in a hash:
if (exists $hash{50} )...
You can delete a certain key-value pair in a hash:
delete($hash{50});
Hash – an associative array
%hash
5"a" >=
"zzz""bob" >=
"John"50 >=
%hash
5"a" >=
"aaa""bob" >=
"John"50 >=
%hash
5"a" >=
"aaa""bob" >=
"John"50 >=
"z"555 >=
%hash
5"a" >=
"aaa""bob" >=
"z"555 >=
8.5 Variable types in PERL
Scalar Array Hash
$number-3.54
$string"hi\n"
@array %hash
>=
>=
>=$array[0]
$hash{key}
8.6
An associative array of the phone book suggested in the first slide
(we will se a more elaborated version later on):
Declare
my %phoneBook;
Updating
$phoneBook{"Dudi"} = 9245;
$phoneBook{"Dudu"} = 7693;
Fetching
print $phoneBook{"Dudi"};
Hash – an associative array
%hash
9245"Dudi" >=
7693"Dudu" >=
8.7
It is possible to get a list of all the keys in %hash
my @hashKeys = keys(%hash);
Similarly you can get an array of the values in %hash
my @hashVals = values(%hash);
Iterating over hash elements
@hashVals
5 "zzz" "John"
@hashKeys
"a" "bob" 50
%hash
5"a" >=
"zzz""bob" >=
"John"50 >=
8.8
To iterate over all the values in %hash
my @hashVals = values(%hash);
foreach my $value (@hashVals)...
To iterate over the keys in %hash
my @hashKeys = keys(%hash);
foreach my $key (@hashKeys)...
Iterating over hash elements
%hash
5"a" >=
"zzz""bob" >=
"John"50 >=
@hashVals
5 "zzz" "John"
@hashKeys
"a" "bob" 50
8.9
For example, iterating over the keys in %hash :
my @hashKeys = keys(%hash);
foreach my $key (@hashKeys) {
print "The key is $key\n";
print "The value is $hash{$key}\n";
}The key is aThe value is 5The key is bobThe value is zzzThe key is 50The value is John
Iterating over hash elements
%hash
5"a" >=
"zzz""bob" >=
"John"50 >=
@hashVals
5 "zzz" "John"
@hashKeys
"a" "bob" 50
8.10
Notably: The elements are given in an arbitrary order,
so if you want a certain order use sort:
my @hashKeys = keys(%hash);
my @sortedHashKeys = sort(@hashKeys);
foreach $key (@sortedHashKeys) {
print "The key is $key\n";
print "The value is $hash{$key}\n";
}
Iterating over hash elements
%hash
5"a" >=
"zzz""bob" >=
"John"50 >=
@hashVals
5 "zzz" "John"
@hashKeys
"a" "bob" 50
8.11
####################################### Purpose: Store names and phone numbers in a hash,# and allow the user to ask for the number of a certain name.# Input: Enter name-number pairs, enter "END" as a name to stop,# then enter a name to get his/her number#use strict;
my %phoneNumbers = ();my $number;
Example – phoneBook.pl #1
8.12
# Ask user for names and numbers and store in a hash
my $name = "";
while ($name ne "END") {
print "Enter a name that will be added to the phone book:\n";
$name = >STDIN>;
chomp $name;
if ($name eq "END") {
last;
}
print "Enter a phone number: \n";
$number = >STDIN>;
chomp $number;
$phoneNumbers{$name} = $number;
}
Example – phoneBook.pl #2
8.13
# Ask for a name and print the corresponding number
$name = "";
while ($name ne "END") {
print "Enter a name to search for in the phone book:\n";
$name = >STDIN>;
chomp $name;
if (exists($phoneNumbers{$name})) {
print "The phone number of $name is: $phoneNumbers{$name}\n";
}
elsif ($name eq "END") {
last;
}
else {
print "Name not found in the book\n";
}
}
Example – phoneBook.pl #3
8.14 Class exercise 81. Write a script that reads a file with a list of protein names and lengths
(proteinLengths ):AP_000081 181AP_000174 104AP_000138 145stores the names of the sequences as hash keys, with the length of the sequence as the value. Print the keys of the hash.
2. Add to Q1: Read another file, and print the names that appeared in both files with the same length. Print a warning if the name is the same but the length is different.
3. Write a script that reads a GenPept file (you may use the preproinsulin record), finds all JOURNAL lines, and stores in a hash the journal name (as key) and year of publication (as value):a. Store only one year value for each journal nameb*. Store all years for each journal name
Then print the names and years, sorted by the journal name (no need to sort the years for the same journal in b*, unless you really want to do so…)