Sortung a structured array on more than one criteria

ruby-talk
1

I can sort an array like that :

results = rs.sort_by{|p| p.km}

but I tried to add a scrond sorting criteria like that :

results = rs.sort_by{|p| p.km, p.updated_at }

and I got obviously an error ... parse error, unexpected '}', expecting tCOLON2 or '[' or '.'

canot find the correct writing..

appreciate any help...

thanks

joss

2

results = rs.sort_by { |p| [p.km, p.updated_at] }

Arrays can be sorted and will compare their contents in order, so this should do what you want.

Hope that helps.

James Edward Gray II

···

On Jan 9, 2007, at 8:30 AM, Josselin wrote:

I can sort an array like that :

results = rs.sort_by{|p| p.km}

but I tried to add a scrond sorting criteria like that :

results = rs.sort_by{|p| p.km, p.updated_at }

3

Hi --

···

On Tue, 9 Jan 2007, Josselin wrote:

I can sort an array like that :

results = rs.sort_by{|p| p.km}

but I tried to add a scrond sorting criteria like that :

results = rs.sort_by{|p| p.km, p.updated_at }

and I got obviously an error ... parse error, unexpected '}', expecting tCOLON2 or '[' or '.'

canot find the correct writing..

Try this:

   results = rs.sort_by {|p| [p.km, p.updated_at] }

David

--
Q. What is THE Ruby book for Rails developers?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black\)
    (See what readers are saying! http://www.rubypal.com/r4rrevs.pdf\)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)

4

results = rs.sort_by{|p| [p.km,p.updated_at]}

Farrel

···

On 09/01/07, Josselin <josselin@wanadoo.fr> wrote:

I can sort an array like that :

results = rs.sort_by{|p| p.km}

but I tried to add a scrond sorting criteria like that :

results = rs.sort_by{|p| p.km, p.updated_at }

and I got obviously an error ... parse error, unexpected '}',
expecting tCOLON2 or '[' or '.'

canot find the correct writing..

appreciate any help...

thanks

joss

5

thanks to both of you... and HNY%2007 (Dry version of Happy New Year 2007) ;-))

I forgot to ask about a DESC sort.... p.km is Ascending and p.updated_at should be DESC..

I am not sure that is possible (at least not documented.....)

joss

···

On 2007-01-09 15:29:43 +0100, Josselin <josselin@wanadoo.fr> said:

I can sort an array like that :

results = rs.sort_by{|p| p.km}

but I tried to add a scrond sorting criteria like that :

results = rs.sort_by{|p| p.km, p.updated_at }

and I got obviously an error ... parse error, unexpected '}', expecting tCOLON2 or '[' or '.'

canot find the correct writing..

appreciate any help...

thanks

joss

6

I can sort an array like that :

results = rs.sort_by{|p| p.km}

but I tried to add a scrond sorting criteria like that :

results = rs.sort_by{|p| p.km, p.updated_at }

Try this.

results = rs.sort_by { |p| [p.km, p.updated_at] }

This way you're sorting arrays containing each of the sort criteria.

···

On Jan 9, 2007, at 8:30 AM, Josselin wrote:

and I got obviously an error ... parse error, unexpected '}', expecting tCOLON2 or '[' or '.'

canot find the correct writing..

7

results = rs.sort_by{|p| p.km, -p.updated_at } # if updated_at is Numeric

or

results = rs.sort { |a,b| [a.km, b.updated_at] <=> [b.km, a.updated_at] }

···

On 1/9/07, Josselin <josselin@wanadoo.fr> wrote:

On 2007-01-09 15:29:43 +0100, Josselin <josselin@wanadoo.fr> said:

> I can sort an array like that :
>
> results = rs.sort_by{|p| p.km}
>
> but I tried to add a scrond sorting criteria like that :
>
> results = rs.sort_by{|p| p.km, p.updated_at }
>
> and I got obviously an error ... parse error, unexpected '}',
> expecting tCOLON2 or '[' or '.'
>
> canot find the correct writing..
>
> appreciate any help...
>
> thanks
>
> joss

thanks to both of you... and HNY%2007 (Dry version of Happy New Year
2007) ;-))

I forgot to ask about a DESC sort.... p.km is Ascending and
p.updated_at should be DESC..

I am not sure that is possible (at least not documented.....)

joss

8

Hi --

···

On Tue, 9 Jan 2007, Josselin wrote:

thanks to both of you... and HNY%2007 (Dry version of Happy New Year 2007) ;-))

Actually Happy New Year 2007 is already pretty DRY, although it does
use two 0's.... :slight_smile: Yours is more like the golf version :slight_smile:

David

--
Q. What is THE Ruby book for Rails developers?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black\)
    (See what readers are saying! http://www.rubypal.com/r4rrevs.pdf\)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)

9

thanks , 'updated_at' is a string ( "2007-01-04 13:48:30")
I try to understand the writing... why the first parameter will be Ascending and the second Descending ...

how would you write it, if both parameters shoudl be Descending ?

Joss

···

On 2007-01-09 15:53:13 +0100, "Jan Svitok" <jan.svitok@gmail.com> said:

On 1/9/07, Josselin <josselin@wanadoo.fr> wrote:

On 2007-01-09 15:29:43 +0100, Josselin <josselin@wanadoo.fr> said:

> I can sort an array like that :
>
> results = rs.sort_by{|p| p.km}
>
> but I tried to add a scrond sorting criteria like that :
>
> results = rs.sort_by{|p| p.km, p.updated_at }
>
> and I got obviously an error ... parse error, unexpected '}',
> expecting tCOLON2 or '[' or '.'
>
> canot find the correct writing..
>
> appreciate any help...
>
> thanks
>
> joss

thanks to both of you... and HNY%2007 (Dry version of Happy New Year
2007) ;-))

I forgot to ask about a DESC sort.... p.km is Ascending and
p.updated_at should be DESC..

I am not sure that is possible (at least not documented.....)

joss

results = rs.sort_by{|p| p.km, -p.updated_at } # if updated_at is Numeric

or

results = rs.sort { |a,b| [a.km, b.updated_at] <=> [b.km, a.updated_at] }

10

Hi --

···

On Wed, 10 Jan 2007, Josselin wrote:

On 2007-01-09 15:53:13 +0100, "Jan Svitok" <jan.svitok@gmail.com> said:

On 1/9/07, Josselin <josselin@wanadoo.fr> wrote:

On 2007-01-09 15:29:43 +0100, Josselin <josselin@wanadoo.fr> said:

> I can sort an array like that :
>
> results = rs.sort_by{|p| p.km}
>
> but I tried to add a scrond sorting criteria like that :
>
> results = rs.sort_by{|p| p.km, p.updated_at }
>
> and I got obviously an error ... parse error, unexpected '}',
> expecting tCOLON2 or '[' or '.'
>
> canot find the correct writing..
>
> appreciate any help...
>
> thanks
>
> joss

thanks to both of you... and HNY%2007 (Dry version of Happy New Year
2007) ;-))

I forgot to ask about a DESC sort.... p.km is Ascending and
p.updated_at should be DESC..

I am not sure that is possible (at least not documented.....)

joss

results = rs.sort_by{|p| p.km, -p.updated_at } # if updated_at is Numeric

or

results = rs.sort { |a,b| [a.km, b.updated_at] <=> [b.km, a.updated_at] }

thanks , 'updated_at' is a string ( "2007-01-04 13:48:30")
I try to understand the writing... why the first parameter will be Ascending and the second Descending ...

how would you write it, if both parameters shoudl be Descending ?

results = rs.sort_by {...}.reverse

David

--
Q. What is THE Ruby book for Rails developers?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black\)
    (See what readers are saying! http://www.rubypal.com/r4rrevs.pdf\)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)

11

Ok, two things:

1. how does my code works:

The block in sort {|x,y| } implements x<=>y (<=>, comparison operator,
sometimes called starship operator, returns -1, 0 or 1 for x <y, x==y
and x> y)

[a,b] <=> [c,d] (array comparision) is implemented as first doing
a<=>c and if they are equal doing b<=>d. if I exchange b and d, I
effectively reverse the result of the second comparision.

If I wanted the reverse sort, I could exchange both pairs, i.e.
instead of doing x<=>y I'd be doing y <=> x.

2. sort_by is usually faster than sort because it does n block
evaluations, while sort does O(n*n) evaluations. Therefore sort_by
{}.reverse is usually better than sort{|a,b| b<=> a} (except some edge
cases where computaton is fast, and the block's result is large)

···

On 1/9/07, dblack@wobblini.net <dblack@wobblini.net> wrote:

Hi --
On Wed, 10 Jan 2007, Josselin wrote:

> On 2007-01-09 15:53:13 +0100, "Jan Svitok" <jan.svitok@gmail.com> said:
>
>> On 1/9/07, Josselin <josselin@wanadoo.fr> wrote:
>>> On 2007-01-09 15:29:43 +0100, Josselin <josselin@wanadoo.fr> said:
>>>
>>> > I can sort an array like that :
>>> >
>>> > results = rs.sort_by{|p| p.km}
>>> >
>>> > but I tried to add a scrond sorting criteria like that :
>>> >
>>> > results = rs.sort_by{|p| p.km, p.updated_at }
>>> >
>>> > and I got obviously an error ... parse error, unexpected '}',
>>> > expecting tCOLON2 or '[' or '.'
>>> >
>>> > canot find the correct writing..
>>> >
>>> > appreciate any help...
>>> >
>>> > thanks
>>> >
>>> > joss
>>>
>>> thanks to both of you... and HNY%2007 (Dry version of Happy New Year
>>> 2007) ;-))
>>>
>>> I forgot to ask about a DESC sort.... p.km is Ascending and
>>> p.updated_at should be DESC..
>>>
>>> I am not sure that is possible (at least not documented.....)
>>>
>>> joss
>>
>> results = rs.sort_by{|p| p.km, -p.updated_at } # if updated_at is Numeric
>>
>> or
>>
>> results = rs.sort { |a,b| [a.km, b.updated_at] <=> [b.km, a.updated_at] }
>
> thanks , 'updated_at' is a string ( "2007-01-04 13:48:30")
> I try to understand the writing... why the first parameter will be Ascending
> and the second Descending ...
>
> how would you write it, if both parameters shoudl be Descending ?

results = rs.sort_by {...}.reverse