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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Perl - map to process every member of a list (array)

Perl's map function (like array_walk in PHP) allows you to do something to every member of a list - thus it often saves you the need to write a loop into your Perl, saves the Perl runtime going back time and again to the interbal byte code generated by the compiler, and can be very efficient.

There aren't a large number of map examples in the training course notes that I use; in Perl there are many ways of doing anything and there are always alternatives but - as appropriate - I do add extra demonstrations in as I present the material. Here - four days into a five day course - are my examples of map so far this week:




@vals = map($_*5,@vals);

Take all the members of a list called @vals, multiply each of them by 5, are return them to a list of the same name (@vals), overwriting the original




$plist = join(", ",map (ucfirst lc, @peeps));

Take each element of the list in @peeps (probably people's names) and convert them all to lower case, then capitalise the first letter of their first name. Join the resulting names together with a space between each of them, and put the resulting single scalar string that results into a variable called $plist




map(printf("%20s %d\n",$_,$counter{$_}),@hio[0..9]);

Take the first ten elements of a list called @hio which in this example contained a sorted list of host computer names) and print out, formatted, the corresponding members of the hash called %counter - which contained elements keyed to those host names, with values which were the number of times that the particular host had accessed our server.

This last example is notable in that it makes no use of (throws away) the list returned by map - which will just be a list of "1" values indicating success - the important result is the effect of the 10 operations of printf
(written 2008-10-09, updated 2008-10-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P208 - Perl - Lists
  [28] Perl for breakfast - (2004-08-25)
  [140] Comparison Chart for Perl programmers - list functions - (2004-12-04)
  [230] Course sizes - beware of marketing statistics - (2005-02-27)
  [240] Conventional restraints removed - (2005-03-09)
  [355] Context in Perl - (2005-06-22)
  [463] Splitting the difference - (2005-10-13)
  [560] The fencepost problem - (2006-01-10)
  [622] Queues and barrel rolls in Perl - (2006-02-24)
  [762] Huge data files - what happened earlier? - (2006-06-15)
  [773] Breaking bread - (2006-06-22)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [968] Perl - a list or a hash? - (2006-12-06)
  [1304] Last elements in a Perl or Python list - (2007-08-16)
  [1316] Filtering and altering Perl lists with grep and map - (2007-08-23)
  [1703] Perl ... adding to a list - end, middle, start - (2008-07-09)
  [1917] Out of memory during array extend - Perl - (2008-12-02)
  [1918] Perl Socket Programming Examples - (2008-12-02)
  [2067] Perl - lists do so much more than arrays - (2009-03-05)
  [2226] Revision / Summary of lists - Perl - (2009-06-10)
  [2295] The dog is not in trouble - (2009-07-17)
  [2484] Finding text and what surrounds it - contextual grep - (2009-10-30)
  [2813] Iterating over a Perl list and changing all items - (2010-06-15)
  [2833] Fresh Perl Teaching Examples - part 2 of 3 - (2010-06-27)
  [2996] Copying - duplicating data, or just adding a name? Perl and Python compared - (2010-10-12)
  [3400] $ is atomic and % and @ are molecular - Perl - (2011-08-20)
  [3548] Dark mornings, dog update, and Python and Lua courses before Christmas - (2011-12-10)
  [3669] Stepping through a list (or an array) in reverse order - (2012-03-23)
  [3870] Writing more maintainable Perl - naming fields from your data records - (2012-09-25)
  [3906] Taking the lead, not the dog, for a walk. - (2012-10-28)
  [3939] Lots of ways of doing the same thing in Perl - list iteration - (2012-12-03)
  [4609] Mapping an array / list without a loop - how to do it in Perl 6 - (2016-01-03)


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Processing all files in a directory - Perl
Text formating for HTML, with PHP
Caen Hill and Olivers Castle
Dont bother to write a Perl program
Perl - map to process every member of a list (array)
What a shock
Perl - Subs, Chop v Chomp, => v ,
Question Mark - Colon operator (Perl and PHP)
Which is your best hotel room?
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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