how to sort a multi-elements array

Discussion in 'Ruby' started by Erwin, May 31, 2008.

1. ErwinGuest

I know how to sort an array with 2 elements... that's the only example
I could fin on Array#sort...
but what if ... I need to sort an array like this one :

anArray = [ [1, "joe", 4], [2, "arthur", 2], [5, "william", 3], [16,
"bob", 1], [20, "ernesto", 17], [27, "julia", 1], [28, "barbara", 2] ]

sorting on third-element (highest ranking) , and second-element
(nickname)

aSortedArray = [ [20, "ernesto", 17], [1, "joe", 4], 5, "william", 3],
[2, "arthur", 2], [28, "barbara", 2], [16, "bob", 1] ]

any doc link where this is explained ?

thanks a lot for your tip

Erwin, May 31, 2008

2. Robert KlemmeGuest

On 31.05.2008 19:31, Erwin wrote:
> I know how to sort an array with 2 elements... that's the only example
> I could fin on Array#sort...
> but what if ... I need to sort an array like this one :
>
> anArray = [ [1, "joe", 4], [2, "arthur", 2], [5, "william", 3], [16,
> "bob", 1], [20, "ernesto", 17], [27, "julia", 1], [28, "barbara", 2] ]
>
> sorting on third-element (highest ranking) , and second-element
> (nickname)
>
> aSortedArray = [ [20, "ernesto", 17], [1, "joe", 4], 5, "william", 3],
> [2, "arthur", 2], [28, "barbara", 2], [16, "bob", 1] ]
>
> any doc link where this is explained ?

As always, use #sort with a block or #sort_by - the number of elements
in those arrays is irrelevant, you just need to decide which elements
you want to pick as sort key.

an_array.sort_by {|a,b,c| [c,b]}
an_array.sort {|(a,b,c),(d,e,f)| [c,b] <=> [f,e]}
an_array.sort do |(a,b,c),(d,e,f)|
x = c <=> f
x == 0 ? b <=> e : x
end

Btw, your data looks like it could benefit from using Struct and also
benefit from the automatically implemented <=>, i.e.

Person = Struct.new :age, :name, osition

an_array = [
Person.new(4, "joe", 1),
Person.new(2, "arthur", 2),
Person.new(3, "william", 5),
]

Kind regards

robert

Robert Klemme, May 31, 2008

3. Stefano CroccoGuest

On Saturday 31 May 2008, Erwin wrote:
> I know how to sort an array with 2 elements... that's the only example
> I could fin on Array#sort...
> but what if ... I need to sort an array like this one :
>
> anArray = [ [1, "joe", 4], [2, "arthur", 2], [5, "william", 3], [16,
> "bob", 1], [20, "ernesto", 17], [27, "julia", 1], [28, "barbara", 2] ]
>
> sorting on third-element (highest ranking) , and second-element
> (nickname)
>
> aSortedArray = [ [20, "ernesto", 17], [1, "joe", 4], 5, "william", 3],
> [2, "arthur", 2], [28, "barbara", 2], [16, "bob", 1] ]
>
> any doc link where this is explained ?
>
> thanks a lot for your tip

You can do this:

aSortedArray = anArray.sort do |a, b|
if a[2] == b[2] then a[1] <=> b[1]
else a[2] <=> b[2]
end
end

If the third element of the two subarrays are equal, then the block returns
the result of the comparison of the second elements (using <=>), otherwise it
returns the result of the comparison of the third elements, again using <=>.

I hope this helps

Stefano

Stefano Crocco, May 31, 2008
4. ErwinGuest

On 31 mai, 19:40, Robert Klemme <> wrote:
> On 31.05.2008 19:31, Erwin wrote:
>
> > I know how to sort an array with 2 elements... that's the only example
> > I could fin on Array#sort...
> > but what if ... I need to sort an array like this one :

>
> > anArray = [ [1, "joe", 4], [2, "arthur", 2], [5, "william", 3], [16,
> > "bob", 1], [20, "ernesto", 17], [27, "julia", 1], [28, "barbara", 2] ]

>
> > sorting on third-element (highest ranking) , and second-element
> > (nickname)

>
> > aSortedArray = [ [20, "ernesto", 17], [1, "joe", 4], 5, "william", 3],
> > [2, "arthur", 2], [28, "barbara", 2], [16, "bob", 1] ]

>
> > any doc link where this is explained ?

>
> As always, use #sort with a block or #sort_by - the number of elements
> in those arrays is irrelevant, you just need to decide which elements
> you want to pick as sort key.
>
> an_array.sort_by {|a,b,c| [c,b]}
> an_array.sort {|(a,b,c),(d,e,f)| [c,b] <=> [f,e]}
> an_array.sort do |(a,b,c),(d,e,f)|
> x = c <=> f
> x == 0 ? b <=> e : x
> end
>
> Btw, your data looks like it could benefit from using Struct and also
> benefit from the automatically implemented <=>, i.e.
>
> Person = Struct.new :age, :name, osition
>
> an_array = [
> Person.new(4, "joe", 1),
> Person.new(2, "arthur", 2),
> Person.new(3, "william", 5),
> ]
>
> Kind regards
>
> robert

thanks Robert , I'll write that in my NoteTaker Ruby book !!

Erwin, Jun 1, 2008
5. Alexey ZilberGuest

Hi,

Was going through these older posts and have a similar question. I
have a nested array that contains a date and a filename. I'm trying to
sort by file date.

The array is in the form:

SortedFiles = [ [200904031109, "filea.txt"], [200904031337,
"fileb.txt"], [200904031110, "filec.xt"] ]

What I was trying to do was:

SortedFiles.sort { |[[a,b],[x,y]] a < x | }

That, unfortunately, did not work. I'm using Ruby 1.8.5 btw. Can anyone
help out?

Thanks,
Alex

Stefano Crocco wrote:
> On Saturday 31 May 2008, Erwin wrote:
>> aSortedArray = [ [20, "ernesto", 17], [1, "joe", 4], 5, "william", 3],
>> [2, "arthur", 2], [28, "barbara", 2], [16, "bob", 1] ]
>>
>> any doc link where this is explained ?
>>
>> thanks a lot for your tip

>
> You can do this:
>
> aSortedArray = anArray.sort do |a, b|
> if a[2] == b[2] then a[1] <=> b[1]
> else a[2] <=> b[2]
> end
> end
>
> If the third element of the two subarrays are equal, then the block
> returns
> the result of the comparison of the second elements (using <=>),
> otherwise it
> returns the result of the comparison of the third elements, again using
> <=>.
>
> I hope this helps
>
> Stefano

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

Alexey Zilber, Apr 7, 2009
6. Christopher DicelyGuest

On 4/6/09, Alexey Zilber <> wrote:
> Hi,
>
> Was going through these older posts and have a similar question. I
> have a nested array that contains a date and a filename. I'm trying to
> sort by file date.
>
> The array is in the form:
>
> SortedFiles = [ [200904031109, "filea.txt"], [200904031337,
> "fileb.txt"], [200904031110, "filec.xt"] ]
>
> What I was trying to do was:
>
> SortedFiles.sort { |[[a,b],[x,y]] a < x | }
>
> That, unfortunately, did not work. I'm using Ruby 1.8.5 btw. Can anyone
> help out?

SortedFiles.sort_by {|date, fname| date}
or:
SortedFiles.sort {|record1,record2| record1[0]<=>record2[0]}

Christopher Dicely, Apr 7, 2009
7. Rick DeNataleGuest

[Note: parts of this message were removed to make it a legal post.]

On Tue, Apr 7, 2009 at 12:31 AM, Christopher Dicely <>wrote:

> On 4/6/09, Alexey Zilber <> wrote:
> > Hi,
> >
> > Was going through these older posts and have a similar question. I
> > have a nested array that contains a date and a filename. I'm trying to
> > sort by file date.
> >
> > The array is in the form:
> >
> > SortedFiles = [ [200904031109, "filea.txt"], [200904031337,
> > "fileb.txt"], [200904031110, "filec.xt"] ]
> >
> > What I was trying to do was:
> >
> > SortedFiles.sort { |[[a,b],[x,y]] a < x | }
> >
> > That, unfortunately, did not work. I'm using Ruby 1.8.5 btw. Can anyone
> > help out?

>
> SortedFiles.sort_by {|date, fname| date}
> or:
> SortedFiles.sort {|record1,record2| record1[0]<=>record2[0]}
>
>

Since you are sorting on the first element of each array you can just use
SortedFiles.sort

Array comparison with another array works by using the comparison of the
first pair of elements which aren't equal, so [1,1] < [2,0] < [2,1]

--
Rick DeNatale