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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.
Splitting data reading code from data processing code - Ruby

An iterator (a.k.a. generator in Python) is a function which returns its results as it calculates them, rather than building them up into a larger structure to return all at once when the function is completed. So where you have a big flow of incoming data, you can handle it as it arrives rather than setting up massive arrays / lists.

Ruby makes very strong use of iterators. You define your iterator function to yield results as it gets them, and then you call your iterator and give it a block of code as an extra parameter. Here's a complete example:

def employees(filename)
   fh = File.new(filename)
   while staff = fh.gets
      yield staff
   end
end
 
def listskills(info)
   els = info.split(/\s+/)
   name = els.shift;
   print "#{name} knows #{els.join(", ")}\n"
end
 
employees("../data/requests.xyz") {|info| listskills(info)}


The exciting thing here is that you have split the code of your data reading phase (in the method "employees") from the code of your data processing phase (in the method "listskills") so that each function performs its own logical task, but they are co-existing / running almost in parallel. It would have been possible to write this code, easily, all as a single loop. But then the reader and processor elements would be forever intertwined, and there would be no easy way of reusing either element in another program.

My example above used a {} block to specify the operations to be performed on each value yielded by the iterator. I could also use a do ... end block. Example of the do-end [here], above example code in our course resources [here].
(written 2011-02-04, updated 2011-02-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
R112 - Ruby - Parallelism
  [2979] Ruby - yield; parallel routines - (2010-10-01)
  [4680] Processing data line by line - iterator in Ruby with yield - (2016-05-19)

R104 - Ruby - Control Structures
  [960] 1st, 2nd, 3rd revisited in Ruby - (2006-12-02)
  [962] Breaking a loop - Ruby and other languages - (2006-12-03)
  [985] Equality in Ruby - == eql? and equal? - (2006-12-14)
  [995] Ruby's case - no break - (2006-12-17)
  [1163] A better alternative to cutting and pasting code - (2007-04-26)
  [1220] for loop - how it works (Perl, PHP, Java, C, etc) - (2007-06-06)
  [1582] Ruby, C, Java and more - getting out of loops - (2008-03-19)
  [1587] Some Ruby programming examples from our course - (2008-03-21)
  [1696] Saying NOT in Perl, PHP, Python, Lua ... - (2008-07-04)
  [1738] Clean code, jump free (Example in Lua) - (2008-08-06)
  [1870] What to do with a huge crop of apples - (2008-11-04)
  [1887] Ruby Programming Course - Saturday and Sunday - (2008-11-16)
  [1891] Ruby to access web services - (2008-11-16)
  [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23)
  [2287] Learning to program in Ruby - examples of the programming basics - (2009-07-15)
  [2471] A short form of if ... then ... else - (2009-10-23)
  [2619] Passing code to procedures and yield in Ruby - (2010-02-02)
  [2711] For loop - checked once, or evety time? Ruby v Perl comparison and contrast - (2010-04-07)
  [2892] Alternative loops and conditionals in Ruby and Perl - (2010-07-28)
  [2975] Why do I need brackets in Ruby ... or Perl, Python, C or Java - (2010-09-29)
  [3158] Ruby training - some fresh examples for string handling applications - (2011-02-05)
  [3159] Returning multiple values from a function call in various languages - a comparison - (2011-02-06)
  [3200] How a for loop works Java, Perl and other languages - (2011-03-12)
  [3253] Is this number between? Does this list include? - Ruby - (2011-04-18)
  [3254] Multiple inputs, multiple out, ruby functions - (2011-04-19)
  [3397] Does a for loop evaluate its end condition once, or on every iteration? - (2011-08-18)
  [3422] Assigning values to variables within other statements - Ruby - (2011-09-07)
  [3619] Ruby v Perl - a comparison example - (2012-02-21)
  [3620] Finding the total, average, minimum and maximum in a program - (2012-02-22)
  [3769] Muttable v immutable and implications - Ruby - (2012-06-20)
  [4322] Learning to Program - the conditional statement (if) - (2014-11-21)
  [4323] Learning to program - Loop statements such as while - (2014-11-22)
  [4370] Conditionals, loops and methods in Ruby - a primer with simple examples - (2014-12-29)
  [4402] Finding sum, minimum, maximum and average in Python (and Ruby) - (2015-01-19)
  [4503] Separating your code for easier testing, understanding and re-use; example in Ruby - (2015-06-02)
  [4504] Where does Ruby load modules from, and how to load from current directory - (2015-06-03)
  [4674] Alternating valuses / flip-flop / toggle - example in Ruby - (2016-05-17)


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Extra courses - Advanced PHP, MySQL and Lua
A new monopoly on the ferry to Northern Ireland
Splitting data reading code from data processing code - Ruby
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Changing a class later on - Ruby
Points West to Belfast
Jargon busting
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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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