Revision / Summary of lists

We've started the third day of this week's Perl course with a revision of some features of lists ... posting here as there are some useful reminders (and I came back later to add more comments!)

# Revision / Summary of lists - Perl

 

$abc = 16;   # single value

@abc = (16,14,12,11,10,8,7,2); # multiple values - a list

 

print "Single value is $abc\n";

print "Single value from \@abc $abc[2] (third element)\n";

print "Whole list \@abc: @abc \n";

 

# ------ Processing lists as a whole via functions;

# ------ grep to FILTER

# ------ map to transform every element

 

print "process whole list ...";

# Regulr expression - a 1 follwed by another character NOT a 0 1 or 2

@teens = grep(/^1[^012]/,@abc);

print "Teenagers are @teens\n";

 

@nextyear = map($_+1,@abc); # Add 1 to each element

push @nextyear,1;

print "Next year ages will be @nextyear\n";

 

# ------ $#listname tells us top index number

 

print "You now have ",$#abc," Children\n";

 

# --------  Handling each element of a list

# ---- use "for" if I need to know the key no.

# ---- use "foreach" if I just want to process content

 

for ($k=0; $k<=$#nextyear; $k++) {   # Start ; end condition; step syntax

  print "Child $k will be $nextyear[$k] next year\n";

  }

 

foreach $kiddo (@nextyear) {

  print "We will have a $kiddo y.o. child\n";

  }

We run public Perl Programming courses 4 to 6 times a year, and various advanced Perl courses regularly but a little less often - see here for details.
(written 2009-06-10)

Associated topics are indexed under

P208 - Perl - Lists
  [3939] Lots of ways of doing the same thing in Perl - list iteration - (2012-12-03)
  [3906] Taking the lead, not the dog, for a walk. - (2012-10-28)
  [3870] Writing more maintainable Perl - naming fields from your data records - (2012-09-25)
  [3669] Stepping through a list (or an array) in reverse order - (2012-03-23)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3400] $ is atomic and % and @ are molecular - Perl - (2011-08-20)
  [2996] Copying - duplicating data, or just adding a name? Perl and Python compared - (2010-10-12)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [2813] Iterating over a Perl list and changing all items - (2010-06-15)
  [2484] Finding text and what surrounds it - contextual grep - (2009-10-30)
  [2295] The dog is not in trouble - (2009-07-17)
  [2067] Perl - lists do so much more than arrays - (2009-03-05)
  [1918] Perl Socket Programming Examples - (2008-12-02)
  [1917] Out of memory during array extend - Perl - (2008-12-02)
  [1828] Perl - map to process every member of a list (array) - (2008-10-09)
  [1703] Perl ... adding to a list - end, middle, start - (2008-07-09)
  [1316] Filtering and altering Perl lists with grep and map - (2007-08-23)
  [1304] Last elements in a Perl or Python list - (2007-08-16)
  [968] Perl - a list or a hash? - (2006-12-06)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [773] Breaking bread - (2006-06-22)
  [762] Huge data files - what happened earlier? - (2006-06-15)
  [622] Queues and barrel rolls in Perl - (2006-02-24)
  [560] The fencepost problem - (2006-01-10)
  [463] Splitting the difference - (2005-10-13)
  [355] Context in Perl - (2005-06-22)
  [240] Conventional restraints removed - (2005-03-09)
  [230] Course sizes - beware of marketing statistics - (2005-02-27)
  [140] Comparison Chart for Perl programmers - list functions - (2004-12-04)
  [28] Perl for breakfast - (2004-08-25)

5651

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