From: Anton Bangratz <tony@...>
Date: 2008-03-04T00:15:24+09:00
Subject: Re: Normal For Loop

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Cory Cory wrote:
[for-loops instead of Array#each and friends]

> a =3D some_array
> minValue =3D 999999
> for(i=3D0; i<a.length && minValue!=3D0; i+=3D1) {
>    minValue =3D (5000 - a[i]).abs
> }
>=20

Break is your friend;
Some solutions for this example:

# No. 1
# (assuming that you are going to process the element, in this case,
# printing it to STDOUT and adding a newline):
a =3D [100, 200, 3000, 5000, 80000] # Arbitrary Array initialisation,
                                  # will be needed for all examples.
a.each {|i|
  break if (5000-i).abs =3D=3D 0
  puts i
}
100
200
3000
    =3D=3D>nil

# No. 2
# returning an array with elements *not* meeting the condition
a.reject { |i| (5000-i).abs =3D=3D 0 } # Can also be used as 'select'
                                   # with inverted condition
    =3D=3D>[100, 200, 3000, 80000]

# No. 3
# returning an array without elements > 5000
a.select { |i| i < 5000 }
    =3D=3D>[100, 200, 3000]

# No. 4
# contrived example, using #map and #compact
# Warning: Don't try this at home
a.map { |i| i < 5000 ? i : nil }.compact
    =3D=3D>[100, 200, 3000]

# No. 5
# contrived example again, this time using 'size' and artificial
# 'index'; using exact condition, so 'unless' is needed instead of
# 'if'. Using puts for 'debug' messages, or instead of processing
# values. Less readable.
a.size.times { |i|
  break unless (5000 - a[i]).abs !=3D 0
  puts a[i]
}
100
200
3000
    =3D=3D>nil


>=20
> This isn't the best example.  However, there are many times like the=20
> loop above where I want to go through the whole thing, but if I find=20
> exactly what I am looking for, I want to bail out early instead of=20
> wasting that processing time.

That's what 'break' is for.

>=20
> Also, I sometimes may want to not actually iterate straight through, bu=
t=20
> browse through the array in some more complex order.

For Array manipulation, selection etc, refer to 'ri Array' - I can't
see how 'C-style for loops' would help there either.

t.

--=20
Anton Bangratz - Key ID 363474D1 - http://tony.twincode.net/
fortune(6):
Signs of crime: screaming or cries for help.
		-- The Brown University Security Crime Prevention Pamphlet


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