Lists, Arrays, and Hashes

Hash Lookup

A hash maps keys to values, and a lookup reads the value for one key.

hash lookup A hash lookup uses a key inside braces to read one stored value.

Hash Lookup

key
hash_lookup.pl
Replay: real traced execution (multi-file project)
use strict;
use warnings;

my %scores = (
    perl => 95,
    go   => 88,
    ruby => 91,
);
my $key = "go";
my $value = $scores{$key};
my $found = exists $scores{$key} ? "yes" : "no";

print "key=$key\n";
print "found=$found\n";
print "value=$value\n";

use strict;
use warnings;

my %scores = (
    perl => 95,
    go   => 88,
    ruby => 91,
);
my $key = "perl";
my $value = $scores{$key};
my $found = exists $scores{$key} ? "yes" : "no";

print "key=$key\n";
print "found=$found\n";
print "value=$value\n";

use strict;
use warnings;

my %scores = (
    perl => 95,
    go   => 88,
    ruby => 91,
);
my $key = "ruby";
my $value = $scores{$key};
my $found = exists $scores{$key} ? "yes" : "no";

print "key=$key\n";
print "found=$found\n";
print "value=$value\n";

  1. %scores ← 3, $key ← go, $value ← 88, $found ← yes

    4my %scores→ 3 = (5    perl => 95,6    go   => 88,7    ruby => 91,8);9my $key→ go = "go"; #@key="perl", "ruby"10my $value→ 88 = $scores{$key}88;11my $found→ yes = exists $scores{$key}88 ? "yes" : "no";1213print "key=$keygo\n";14print "found=$foundyes\n";15print "value=$value88\n";
    outputkey=go
found=yes
value=88

  1. %scores ← 3, $key ← perl, $value ← 95, $found ← yes

    4my %scores→ 3 = (5    perl => 95,6    go   => 88,7    ruby => 91,8);9my $key→ perl = "perl";10my $value→ 95 = $scores{$key}95;11my $found→ yes = exists $scores{$key}95 ? "yes" : "no";1213print "key=$keyperl\n";14print "found=$foundyes\n";15print "value=$value95\n";
    outputkey=perl
found=yes
value=95

  1. %scores ← 3, $key ← ruby, $value ← 91, $found ← yes

    4my %scores→ 3 = (5    perl => 95,6    go   => 88,7    ruby => 91,8);9my $key→ ruby = "ruby";10my $value→ 91 = $scores{$key}91;11my $found→ yes = exists $scores{$key}91 ? "yes" : "no";1213print "key=$keyruby\n";14print "found=$foundyes\n";15print "value=$value91\n";
    outputkey=ruby
found=yes
value=91

Look Up a Key

  1. %scores stores scores for perl, go, and ruby.
  2. $key is go.
  3. exists $scores{$key} reports yes.
  4. $scores{$key} reads the value 88. | Key | Value | | --- | --- | | perl | 95 | | go | 88 | | ruby | 91 |

Exercise: hash_lookup.pl

Look up one hash key, print whether it exists, and print its value