LING/C SC/PSYC 438/538

1. LING/C SC/PSYC 438/538 Lecture 4 9/5 Sandiway Fong

2. Continuing with Perl • Learn Perl • Books… • Online resources • http://learn.perl.org/ • we begin with ... • http://perldoc.perl.org/perlintro.html

3. O'Reilly's Safari library • UA free access: • http://proquest.safaribooksonline.com.ezproxy2.library.arizona.edu/search?q=perl

4. Perl arrays and hashes • Scalars: • strings, numbers (integers, floating point numbers), references • Arrays: • Idea: list of scalars • Access by index: 0,1,2,… • Hash: • Like an array except access not through a numeric index • Use user-specified keys $variable @variable %variable different namespaces: $apple @apple %apple are different data structures and can co-exist simultaneously

5. Perl Arrays • Arrays: • Idea: list of scalars • Access by index: 0,1,2,… • Notes on output • print @a zeroonetwothreefour • print “@a” zero one two three four • negative indices count from the end.. • $#name (index of last element) • @name (can have scalar interpretation) controlled by system variable $” default value: a space

6. Perl arrays • List operations:

7. Perl Arrays • Last time: • by default sort works according to the ASCII chart, character by character asciitable.com

8. Perl Arrays • Numeric sort? • Idea: to pass an inline comparison function as parameter…

9. Perl Arrays • Getting user input into your program: @ARGV

10. Perl Hashes

11. Perl Hashes • Notes on arrays and hashes • arrays are indexed from 0,1,2,3… • hashes are like arrays with user-defined indexing (aka associative array or hash table) • initialization (use list notation (or shortcut): round brackets and commas) • @a = (“zero”, “one”, “two”, “three”, “four”); • %h = (“zero”, 0, “one”, 1, “two”, 2, “three”, 3, “four”, 4}; (key/value pairs) • access to individual elements (square brackets vs. curly braces) • $a[1] “one” • $h{zero} 0 Shortcut:

12. Perl Hashes • Notes on arrays and hashes • output • print @a zeroonetwothreefour • print “@a” zero one two three four • print %h three3one1zero0two2four4 (note: different order) • print “%h” %h (literal, no interpolation done) What happens here? • %pos = ("apple", "n", "speak", "v", "happy", "a", "walk", "n", "walk", "v"); • print $pos{"walk"}, "\n"; • (hash keys are unique)

13. Perl Hashes • Conditionals • if ( @a < 10 ) { print “Small array\n” } else {print “Big array\n” } • Note: @a here is a scalar = size of array • unless (@a > 10) { print “@a\n” } • Note: if size of array a is ≤ 10, it prints the contents of array a • Looping • %fruits = ("apple", "green", "orange", "orange", "lemon", "yellow"); • foreach $fruit (keys %fruits) { print $fruit, " => ", $fruits{$fruit}, "\n” } gives output: • lemon => yellow • apple => green • orange => orange • Note:keys %fruits = (“lemon” “apple” “orange”) produces a list

14. Perl Hashes • Sorting sort byage keys %age