1. LING/C SC/PSYC 438/538
Lecture 7
Sandiway Fong

2. Today Topics Algorithmic thinking: a worked example Perl References
Perl Modules: cpanm
Reminder:
first programming homework due tomorrow at midnight!

3. RFPerl…
I am a 3rd year doctoral student in the Accounting department. I am looking for a graduate student that is able to write a simple perl script for me. After speaking with individuals who are familiar with coding, it is my understanding that my task is a simple task for someone who is proficient at perl. I am coauthoring a project with a professor in the department and I can offer compensation to the student. Could you send me an of a student who would be able and interested?
Spencer Young

4. Case study: Repeated Word Detection
Microsoft Word:

5. Case study: Repeated Word Detection
Key: think algorithmically…
think of a specific example first w1 w2 w3 w4 w5
Compare w1 with w2
Compare w2 with w3
Compare w3 with w4
Compare w4 with w5

6. Case study: Repeated Word Detection
Generalize specific example, then code it up
Array indices start from 0… w1 w2 w3 …
wn-1 wn
Compare w1 with w1+1
words0 ,words1 … wordsn-1
Compare w2 with w2+1
“for” loop
implementation …
Compare wn-2 with wn-2+1
Array indices end just before $#words…
Compare wn-1 with wn

7. Case study: Repeated Word Detection

8. Case study: Repeated Word Detection

9. Case study: Repeated Word Detection

10. Case study: Repeated Word Detection

11. Case study: Repeated Word Detection

12. Case study: Repeated Word Detection

13. Case study: Repeated Word Detection
a decent first pass …

14. Case study: Repeated Word Detection
Sample data file:
Output:

15. Case study: Repeated Word Detection
Second try.. merging multiple occurrences
Sample data file:
Output:

16. Case study: Repeated Word Detection
Second try.. merging multiple occurrences

17. Case study: Repeated Word Detection
Third try.. implementing a simple table of exceptions

18. Case study: Repeated Word Detection
Third try.. table of exceptions
Sample data file:
Output:
Grammar, very, very, very big error

19. More complex data structures
Arrays and hashes may only contain scalars
Question: How to accomplish nesting, i.e. put non-scalars inside?
Answer: use references (pointers), which happen to be scalars
perlreftut.html
(actually a reference is just an unsigned number: computer address)

20. References Two ways to make a reference:
Remember bracketing when initializing:
( ) List – can be used for both arrays and hashes
[] Reference to an array
{} Reference to a hash
Two ways to make a reference:

21. References Let’s figure out what the following mean:
Example: array of arrays
Note: uses Make Rule 2: square brackets
Let’s figure out what the following mean:
de-reference

22. References Looping (using for/foreach) with array/hash references:
Careful! $aref->[3] and $aref[3] are different

23. References Perl code: What happens here? $a = [1, 2, 3, 4, 5];
print $a+1, "\n";
What happens here?

24. References Looping (using for/foreach) with array/hash references:
Careful! $href->{‘red’} and $href{‘red’} are different.

25. CPAN Minus https://www.cpan.org Various installers for Perl modules:
cpanm (CPAN Minus)
install (various ways)
cd ~/bin (a directory where you want it to be)
curl -L -o cpanm
chmod +x cpanm
cpan
cpanp

26. CPAN Minus
Ubuntu:
Ubuntu: sudo apt-get cpanminus

27. Where are Perl modules stored?
@INC array variable
perl -e 'print "$_\n"
/opt/local/lib/perl5/site_perl/5.24/darwin-thread-multi-2level
/opt/local/lib/perl5/site_perl/5.24
/opt/local/lib/perl5/vendor_perl/5.24/darwin-thread-multi-2level
/opt/local/lib/perl5/vendor_perl/5.24
/opt/local/lib/perl5/5.24/darwin-thread-multi-2level
/opt/local/lib/perl5/5.24 .
perldoc -lm Lingua::EN::CMUDict (from lecture2) /opt/local/lib/perl5/site_perl/5.24/Lingua/EN/CMUDict.pm

28. Example: a day of week calculator
dow.perl
perl dow.perl
Can't locate Date/Calc.pm (you may need to install the Date::Calc module) contains: /opt/local/lib/perl5/site_perl/5.24/dar win-thread-multi-2level /opt/local/lib/perl5/site_perl/5.24 /opt/local/lib/perl5/vendor_perl/5.24/d arwin-thread-multi-2level /opt/local/lib/perl5/vendor_perl/5.24 /opt/local/lib/perl5/5.24/darwin- thread-multi-2level /opt/local/lib/perl5/5.24 .) at dow.perl line 1. BEGIN failed--compilation aborted at dow.perl line 1.

29. Example: a day of week calculator
sudo cpanm Date::Calc Password: --> Working on Date::Calc Fetching OK Configuring Date-Calc OK ==> Found dependencies: Bit::Vector, Carp::Clan --> Working on Bit::Vector Fetching OK Configuring Bit-Vector OK ==> Found dependencies: Carp::Clan --> Working on Carp::Clan Fetching OK Configuring Carp-Clan OK ==> Found dependencies: Test::Exception --> Working on Test::Exception Fetching OK
Configuring Test-Exception OK ==> Found dependencies: Sub::Uplevel --> Working on Sub::Uplevel Fetching OK Configuring Sub-Uplevel OK Building and testing Sub-Uplevel OK Successfully installed Sub-Uplevel Building and testing Test-Exception OK Successfully installed Test-Exception-0.43 Building and testing Carp-Clan OK Successfully installed Carp-Clan-6.06 Building and testing Bit-Vector OK Successfully installed Bit-Vector-7.4 Building and testing Date-Calc OK Successfully installed Date-Calc distributions installed
perldoc -lm Date::Calc
/opt/local/lib/perl5/site_perl/5.24/Date/Calc.pm

30. Example: a day of week calculator
perl dow.perl usage: month day year perl dow.perl /12/2017 falls on a Tuesday perl dow.perl /12/2016 falls on a Monday

31. localtime
Date::Calc
also Now()
Built-in:
all numbers