Hi,

I'm looking for an elegant way to do the following:

Given an sorted array of (X,Y) pairs where Y is strictly
increasing, i.e., no repeated Ys.

Compact pairs with repeated Xs, keeping the pair with
the highest Y value.

E.g.,

require 'test/unit'

class TestConsolidation < Test::Unit::TestCase
def test_should_remove_repeated_Xs_but_save_one_with_h ighest_Y
initial = [ [ 1, 12 ], [ 3, 15 ], [ 3, 17 ], [ 3, 22 ], [ 7, 45 ] ]
desired = [ [ 1, 12 ], [ 3, 22 ], [ 7, 45 ] ]
assert_equal desired, initial.consolidate
end
end

class Array
def consolidate
# Too embarrassed to show current hack.
end
end

My least surprise inclination had me researching #uniq and #compact
to see if they took a block like #sort.

Thanks,
--
Bil Kleb
http://fun3d.larc.nasa.gov

2008/1/7, Bil Kleb <Bil.Kleb@nasa.gov>:
> I'm looking for an elegant way to do the following:
> (...)

Bil, this makes the test pass:

class Array
def consolidate
Hash[*flatten].sort
end
end

Regards,
Pit

2008/1/7, Bil Kleb <Bil.Kleb@nasa.gov>:
> Hi,
>
> I'm looking for an elegant way to do the following:
>
> Given an sorted array of (X,Y) pairs where Y is strictly
> increasing, i.e., no repeated Ys.
>
> Compact pairs with repeated Xs, keeping the pair with
> the highest Y value.
>
> E.g.,
>
> require 'test/unit'
>
> class TestConsolidation < Test::Unit::TestCase
> def test_should_remove_repeated_Xs_but_save_one_with_h ighest_Y
> initial = [ [ 1, 12 ], [ 3, 15 ], [ 3, 17 ], [ 3, 22 ], [ 7, 45 ] ]
> desired = [ [ 1, 12 ], [ 3, 22 ], [ 7, 45 ] ]
> assert_equal desired, initial.consolidate
> end
> end
>
> class Array
> def consolidate
> # Too embarrassed to show current hack.
> end
> end
>
> My least surprise inclination had me researching #uniq and #compact
> to see if they took a block like #sort.

This is easy with #inject:

ar.inject([]) do |res, (x,y)|
if res.empty? || res.last[0] != x
res << [x,y]
else
res.last[1] = y
end
res
end

Cheers

robert

--
use.inject do |as, often| as.you_can - without end

Pit Capitain wrote:
> 2008/1/7, Bil Kleb <Bil.Kleb@nasa.gov>:
>> I'm looking for an elegant way to do the following:
>> (...)
>
> Bil, this makes the test pass:
>
> class Array
> def consolidate
> Hash[*flatten].sort
> end
> end

That certainly is elegant!

Maybe Bil wanted to preserve the monotonicity?

class Array
def consolidate
Hash[*flatten].sort_by {|x,y| y}
end
end

p [ [5,1] , [3,2] ].consolidate # ==> [[5, 1], [3, 2]]

--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

A more general solution:

require 'set'

class Array
def uniq(&blk)
blk ||= lambda {|x| x}
already_seen = Set.new
uniq_array = []

self.each_with_index do |value, i|
x = blk.call(value)
unless already_seen.include? x
already_seen << x
uniq_array << value
end
end
uniq_array
end
end

and

class Array
def consolidate
reverse.uniq {|a| a.first}.reverse
end
end

Of course, the value that you keep for uniq is kinda arbitrary.

Dan
- Hide quoted text -

On 1/7/08, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
> Pit Capitain wrote:
> > 2008/1/7, Bil Kleb <Bil.Kleb@nasa.gov>:
> >> I'm looking for an elegant way to do the following:
> >> (...)
> >
> > Bil, this makes the test pass:
> >
> > class Array
> > def consolidate
> > Hash[*flatten].sort
> > end
> > end
>
> That certainly is elegant!
>
> Maybe Bil wanted to preserve the monotonicity?
>
> class Array
> def consolidate
> Hash[*flatten].sort_by {|x,y| y}
> end
> end
>
> p [ [5,1] , [3,2] ].consolidate # ==> [[5, 1], [3, 2]]
>
> --
> vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407
>
>

On Jan 7, 10:45 am, Robert Klemme <shortcut...@googlemail.com> wrote:
>
> This is easy with #inject:

Hey, thanks everyone for the !

I would have replied sooner, but my USENET feed dropped your replies
and I only now thought to look at groups.google.com.

Thanks again,
--
http://twitter.com/bil_kleb