Sorting an array based on two attributes of objects

ruby-talk
1

Thanks for some of your replies for the lst post i need small
modification in that post .. i want to sort the salary in descending
order. i have explained the same quesion again....

Hi all,
     I want to sort the objects of array based on two attributes.I want
sort an employee class based on his salary in descecding order and name
, so that if two
person has same salary it should be sorted with name.
     Lets say for example the employee objects has following name and
salary.

         name salary
           d 100
           c 200
           b 50
           a 100

     so in this case the result which i expect is

         name salary
           b 200
           a 100
           d 100
           c 50

  Note:In the above example for salary 100 the sorting is done
alphabetically, but initially(before sorting) 'd' came first and then
'a' came.so basically i want to sort the array with more than one order.
  Can any one help me to solve it ??

···

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Posted via http://www.ruby-forum.com/.

2

senthil wrote:

Thanks for some of your replies for the lst post i need small
modification in that post .. i want to sort the salary in descending
order. i have explained the same quesion again....

Hi all,
     I want to sort the objects of array based on two attributes.I want
sort an employee class based on his salary in descecding order and name
, so that if two
person has same salary it should be sorted with name.
     Lets say for example the employee objects has following name and
salary.

         name salary
           d 100
           c 200
           b 50
           a 100

     so in this case the result which i expect is

         name salary
           b 200
           a 100
           d 100
           c 50

  Note:In the above example for salary 100 the sorting is done
alphabetically, but initially(before sorting) 'd' came first and then
'a' came.so basically i want to sort the array with more than one order.
  Can any one help me to solve it ??

In this case, just invert the salary:

sorted_employees = employees.sort_by { |e| [ -e.salary, e.name ] }

I can't think of a way offhand to have different lexicographic orderings in the same sort, though.

···

--
Alex

3

senthil wrote:

Thanks for some of your replies for the lst post i need small
modification in that post .. i want to sort the salary in descending
order. i have explained the same quesion again....

I came up with this which is sub par as I test for a condition twice so
stay tuned for a better solution..

irb(main):001:0> [['d',100],['c',200],['b',50],['a',100]].sort {|a,b|
b[1]==a[1]?a[0]<=>b[0]:b[1]<=>a[1]}
=> [["c", 200], ["a", 100], ["d", 100], ["b", 50]]

hope this helps

ilan

···

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Posted via http://www.ruby-forum.com/\.

4

Alex Young wrote:

sorted_employees = employees.sort_by { |e| [ -e.salary, e.name ] }

I can't think of a way offhand to have different lexicographic orderings
in the same sort, though.

Doh!!!! Ofcourse! Ok.. more coffee for me..

<sulks away with his tail between his legs>

ilan

···

--
Posted via http://www.ruby-forum.com/\.

5

Just to add a bit to this: consider using .nonzero? for chained comparisons

[['d',100],['c',200],['b',50],['a',100]].
   sort {|a,b| (b[1]<=>a[1]).nonzero? || a[0]<=>b[0] }

-Rob

Rob Biedenharn http://agileconsultingllc.com
Rob@AgileConsultingLLC.com

···

On Mar 26, 2007, at 10:18 AM, Ilan Berci wrote:

senthil wrote:

Thanks for some of your replies for the lst post i need small
modification in that post .. i want to sort the salary in descending
order. i have explained the same quesion again....

I came up with this which is sub par as I test for a condition twice so
stay tuned for a better solution..

irb(main):001:0> [['d',100],['c',200],['b',50],['a',100]].sort {|a,b|
b[1]==a[1]?a[0]<=>b[0]:b[1]<=>a[1]}
=> [["c", 200], ["a", 100], ["d", 100], ["b", 50]]

hope this helps

ilan

6

Someone, in another recent thread, came up with the idea of a reverse
proxy class something like this

class Reverse

   :attr_reader :obj

   def initialize(obj)
      @obj = obj
   end

   def <=>(other)
       other.obj <=> self.obj
   end

end

so let's say you wanted to sort the names in descending order as well:
sorted_employees = employees.sort_by { |e| [-e.salary, Reverse.new(e.name) ] }

You could even use this "reverse" proxy to change the sorting of
salary, so that the original could be:

sorted_employees = employees.sort_by { |e| [ Reverse.new(e.salary), e.name ] }

One could quibble about the name Reverse.

···

On 3/26/07, Alex Young <alex@blackkettle.org> wrote:

senthil wrote:
> Thanks for some of your replies for the lst post i need small
> modification in that post .. i want to sort the salary in descending
> order. i have explained the same quesion again....
>
> Hi all,
> I want to sort the objects of array based on two attributes.I want
> sort an employee class based on his salary in descecding order and name
> , so that if two
> person has same salary it should be sorted with name.
> Lets say for example the employee objects has following name and
> salary.
>
> name salary
> d 100
> c 200
> b 50
> a 100
>
> so in this case the result which i expect is
>
> name salary
> b 200
> a 100
> d 100
> c 50
>
> Note:In the above example for salary 100 the sorting is done
> alphabetically, but initially(before sorting) 'd' came first and then
> 'a' came.so basically i want to sort the array with more than one order.
> Can any one help me to solve it ??
>
In this case, just invert the salary:

sorted_employees = employees.sort_by { |e| [ -e.salary, e.name ] }

I can't think of a way offhand to have different lexicographic orderings
in the same sort, though.

--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

7

Rick DeNatale wrote:
<snip>

In this case, just invert the salary:

sorted_employees = employees.sort_by { |e| [ -e.salary, e.name ] }

I can't think of a way offhand to have different lexicographic orderings
in the same sort, though.

Someone, in another recent thread, came up with the idea of a reverse
proxy class something like this

class Reverse

  :attr_reader :obj

  def initialize(obj)
     @obj = obj
  end

  def <=>(other)
      other.obj <=> self.obj
  end

end

so let's say you wanted to sort the names in descending order as well:
sorted_employees = employees.sort_by { |e| [-e.salary, Reverse.new(e.name) ] }

You could even use this "reverse" proxy to change the sorting of
salary, so that the original could be:

sorted_employees = employees.sort_by { |e| [ Reverse.new(e.salary), e.name ] }

That's lovely. My brain wandered off down the String#invert route, and I ended up getting tied in knots over multibyte encodings. Reverse is a *much* nicer trick.

···

On 3/26/07, Alex Young <alex@blackkettle.org> wrote:

--
Alex