Arrays

## Learning Objectives - Master array manipulation - Use list operations - Work with map and grep - Sort arrays effectively - Understand array context ## Array Basics ### Creating Arrays ```perl use strict; use warnings; my @empty; my @nums = (1, 2, 3, 4, 5); my @mixed = ("hello", 42, 3.14); my @range = (1 .. 10); my @letters = ('a' .. 'z'); ``` ### Array Size ```perl my @colors = ("red", "green", "blue"); print scalar @colors; # 3 (number of elements) print $#colors; # 2 (last index) ``` ### Accessing Elements ```perl my @fruits = ("apple", "banana", "cherry"); print $fruits[0]; # "apple" print $fruits[-1]; # "cherry" (last element) print $fruits[-2]; # "banana" (second to last) # Modify $fruits[0] = "apricot"; ``` ## List Operations ### Push and Pop ```perl my @stack = (1, 2, 3); push @stack, 4; # (1, 2, 3, 4) my $popped = pop @stack; # Returns 4, @stack = (1, 2, 3) unshift @stack, 0; # (0, 1, 2, 3) my $shifted = shift @stack; # Returns 0, @stack = (1, 2, 3) ``` ### splice ```perl my @nums = (1, 2, 3, 4, 5); # Remove and replace splice @nums, 1, 2, (10, 20); # (1, 10, 20, 4, 5) # Just remove splice @nums, 0, 2; # Returns (1, 10), @nums = (20, 4, 5) # Just insert splice @nums, 1, 0, (30, 40); # Insert at position 1 ``` ### join and split ```perl my @words = ("Hello", "World", "Perl"); my $sentence = join " ", @words; print $sentence; # "Hello World Perl" my $line = "apple,banana,cherry"; my @fruits = split ",", $line; print "@fruits"; # apple banana cherry # Split with limit my @parts = split ":", "a:b:c:d", 2; # ("a", "b:c:d") ``` ### reverse ```perl my @nums = (1, 2, 3, 4, 5); my @reversed = reverse @nums; # (5, 4, 3, 2, 1) my @chars = split "", "hello"; my @rev_chars = reverse @chars; my $rev_string = join "", @rev_chars; # "olleh" ``` ## map ### Basic map ```perl use strict; use warnings; my @nums = (1, 2, 3, 4, 5); # Square each number my @squares = map { $_ * $_ } @nums; print "@squares\n"; # 1 4 9 16 25 # Transform strings my @names = ("alice", "bob", "charlie"); my @caps = map { ucfirst lc $_ } @names; print "@caps\n"; # Alice Bob Charlie ``` ### map with Multiple Expressions ```perl my %hash = ( a => 1, b => 2, c => 3, ); # Double values my %doubled = map { $_, $hash{$_} * 2 } keys %hash; print "$_ => $doubled{$_}\n" for keys %doubled; ``` ### map vs foreach ```perl # map returns transformed list my @squares = map { $_ * $_ } (1 .. 5); # foreach just iterates foreach my $num (1 .. 5) { print "$num "; } ``` ## grep ### Basic grep ```perl use strict; use warnings; my @nums = (1, 2, 3, 4, 5, 6, 7, 8, 9, 10); # Find even numbers my @evens = grep { $_ % 2 == 0 } @nums; print "@evens\n"; # 2 4 6 8 10 # Find numbers greater than 5 my @big = grep { $_ > 5 } @nums; print "@big\n"; # 6 7 8 9 10 ``` ### grep with Regex ```perl my @words = ("apple", "banana", "apricot", "cherry", "avocado"); # Words starting with 'a' my @a_words = grep { /^a/ } @words; print "@a_words\n"; # apple apricot avocado # Words containing 'an' my @an_words = grep { /an/ } @words; print "@an_words\n"; # banana apricot ``` ### grep vs grep not ```perl my @nums = (1, 2, 3, 4, 5); my @small = grep { $_ < 4 } @nums; # 1, 2, 3 my @not_small = grep { $_ >= 4 } @nums; # 4, 5 ``` ## sort ### Basic sort ```perl use strict; use warnings; my @nums = (3, 1, 4, 1, 5, 9, 2, 6); my @sorted = sort @nums; print "@sorted\n"; # 1 1 2 3 4 5 6 9 (string sort!) # String sort my @words = ("banana", "apple", "cherry"); my @alpha = sort @words; print "@alpha\n"; # apple banana cherry ``` ### Numeric Sort ```perl my @nums = (3, 1, 4, 1, 5, 9, 2, 6); my @sorted = sort { $a <=> $b } @nums; print "@sorted\n"; # 1 1 2 3 4 5 6 9 # Reverse numeric my @rev = sort { $b <=> $a } @nums; print "@rev\n"; # 9 6 5 4 3 2 1 1 ``` ### Custom Sort ```perl # By length my @words = ("apple", "hi", "banana", "a", "cherry"); my @by_len = sort { length($a) <=> length($b) } @words; print "@by_len\n"; # a hi apple banana cherry # Case-insensitive sort my @mixed = ("Apple", "banana", "Cherry"); my @sorted = sort { lc($a) cmp lc($b) } @mixed; print "@sorted\n"; # Apple banana Cherry # Stable sort (preserve order of equals) ``` ### Sort Hash Keys/Values ```perl my %scores = ( Alice => 95, Bob => 87, Charlie => 92, ); # Sort by values my @by_score = sort { $scores{$a} <=> $scores{$b} } keys %scores; print "@by_score\n"; # Bob Charlie Alice ``` ## Advanced Array Operations ### List Assignment ```perl my ($first, $second, @rest) = (1, 2, 3, 4, 5); print "$first, $second, @rest\n"; # 1, 2, 3 4 5 # Swap values my ($x, $y) = (10, 20); ($x, $y) = ($y, $x); # Swap! ``` ### List as Return Value ```perl sub get_range { return (1 .. 10); } my @nums = get_range(); # (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) ``` ### Flattening ```perl my @a = (1, 2); my @b = (3, 4); my @combined = (@a, @b); # (1, 2, 3, 4) # Nested arrays flatten my @nested = (1, [2, 3], 4); # Actually (1, 2, 3, 4) in list context ``` ### List Context ```perl # Force list context my @copy = (1, 2, 3); # In scalar context, last value my $last = (1, 2, 3); # $last = 3 # Force scalar with scalar() my $count = scalar @array; ``` ## Reducing Arrays ### Manual Reduction ```perl sub sum { my $total = 0; foreach my $val (@_) { $total += $val; } return $total; } print sum(1, 2, 3, 4, 5); # 15 ``` ### Using reduce (List::Util) ```perl use List::Util qw(reduce); my $sum = reduce { $a + $b } 1, 2, 3, 4, 5; my $product = reduce { $a * $b } 1 .. 5; ``` ## Summary - Arrays created with `@` sigil and parentheses - `$#array` gives last index, `scalar @array` gives length - Push/pop work on end, shift/unshift on beginning - `splice` for advanced insertion/removal - `map` transforms each element - `grep` filters elements by condition - `sort` orders elements (use `<=>` for numeric) - `reverse` reverses list order - `join` combines, `split` breaks apart - Lists flatten in list context