Dynamic variables in loop

Question

I have this working code. I think this must be easier with a while loop.

if not c.e1.nil?
  extrapreis = number_to_currency Extra.find(c.e1).aufschlag, :unit=>"EUR "
  array.push Extra.find(c.e1).name + " (" + extrapreis.to_s + ")"
  extpreis = extpreis + Extra.find(c.e1).aufschlag
end
if not c.e2.nil?
  extrapreis = number_to_currency Extra.find(c.e2).aufschlag, :unit=>"EUR "
  array.push Extra.find(c.e2).name + " (" + extrapreis.to_s + ")"
  extpreis = extpreis + Extra.find(c.e2).aufschlag
end
if not c.e3.nil?
  extrapreis = number_to_currency Extra.find(c.e3).aufschlag, :unit=>"EUR "
  array.push Extra.find(c.e3).name + " (" + extrapreis.to_s + ")"
  extpreis = extpreis + Extra.find(c.e3).aufschlag
end
if not c.e4.nil?
  extrapreis = number_to_currency Extra.find(c.e4).aufschlag, :unit=>"EUR "
  array.push Extra.find(c.e4).name + " (" + extrapreis.to_s + ")"
  extpreis = extpreis + Extra.find(c.e4).aufschlag
end
if not c.e5.nil?
  extrapreis = number_to_currency Extra.find(c.e5).aufschlag, :unit=>"EUR "
  array.push Extra.find(c.e5).name + " (" + extrapreis.to_s + ")"
  extpreis = extpreis + Extra.find(c.e5).aufschlag          
end

It is always the same code, except for the variable e (1, 2, 3, 4, 5). How can I put this in a while loop and put the counter together with e?

sawa · Accepted Answer · 2013-01-06 21:27:04Z

up vote 1 down vote accepted

(1..5).each do |i|
  e = c.send("e#{i}")
  next if e.nil?
  found = Extra.find(e)
  array.push("#{found.name} (#{number_to_currency(found.aufschlag, unit: "EUR ")})")
  extpreis += found.aufschlag
end

If you can be certain that c.e1 etc. never becomes false, then:

(1..5).each do |i|
  next unless e = c.send("e#{i}")
  found = Extra.find(e)
  array.push("#{found.name} (#{number_to_currency(found.aufschlag, unit: "EUR ")})")
  extpreis += found.aufschlag
end

answered Jan 6 '13 at 21:27

sawa
24914

Thank you very much. So I learn a little more about rails ;) – user1953483 Jan 6 '13 at 21:40

It is not Rails. It's all plain Ruby. Actually, I barely know anything about Rails. – sawa Jan 6 '13 at 21:42

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the Tin Man · Answer 2 · 2013-01-06 21:15:02Z

up vote 1 down vote

I'd start with this untested code:

[c.e1, c.e2, c.e3, c.e4, c.e5].each do |e|
  if e
    extrapreis = number_to_currency(Extra.find(e).aufschlag, unit: 'EUR ')
    array << Extra.find(e).name + ' (' + extrapreis.to_s + ')'
    extpreis += Extra.find(e).aufschlag
  end
end

answered Jan 6 '13 at 21:15

the Tin Man
24819

Maybe unless instead of if !? – Andy H Jan 6 '13 at 21:17

I don't like unless, especially at the start of a conditional block. It's one of those programmer-choice, often argued, syntax things. – the Tin Man Jan 6 '13 at 21:20

Fair enough - in fact this article would advocate a simple if e instead :) – Andy H Jan 6 '13 at 21:24

That's true, if e is how I'd normally write it if I was doing a refactor or review. :-) I'll adjust it. Thanks. – the Tin Man Jan 6 '13 at 21:36

1

You'd probably like Ruby Best Practices – the Tin Man Jan 6 '13 at 21:39

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tokland · Answer 3 · 2013-01-07 18:30:56Z

Notes on your code:

Use of parentheses: Ruby allows you to drop them, but the community seems to have reached a consensus it may harm readability, restrict its usage to DSL-style code.
extrapreis: this may be "private" code (well, it's not anymore since you publicly asked about it), but it's good practice to use the commonly accepted language in the programming world (for script names, variable names, comments, everything).
array.push, x = x + y, ...: you may use this but being aware about functional programming and why inplace updates are considered (by some) bad practice. More on this issue.
if not c.e1.nil? -> if c.e1.
Extra.find(c.e1).aufschlag. In each block you call this twice, why? use a variable to store the value.

For a novice programmer a functional approach may be a little difficult to grasp at first, but it introduces important concepts that will (hopefully) prove useful later on:

strings, values = [c.e1, c.e2, c.e3, c.e4].compact.map do |e|
  value = Extra.find(e).aufschlag
  extra_price = number_to_currency(value, :unit => "EUR")
  name = Extra.find(e).name 
  ["#{name} (#{extra_price})", value]
end.transpose
extra_price_total = values.inject(0, :+)

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