Sorting an array based on two attributes of objects

Ruby
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 ??

2

senthil wrote:

salary.
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.

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

4

Alex Y. 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…

ilan

5

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

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

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 B. http://agileconsultingllc.com
[email protected]

6

On 3/26/07, Alex Y. [email protected] wrote:

 Lets say for example the employee objects has following name and

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 ] }

One could quibble about the name Reverse.

–
Rick DeNatale

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

7

Rick DeNatale wrote:

On 3/26/07, Alex Y. [email protected] wrote:

class Reverse

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.