I am comparing two arrays with:
original_item_ids.sort <=> new_item_ids.sort
However, this returns nil, which seems to be against the documentation
which says the result will be -1, 0 or 1. Both arrays contain the same
values, alhough in a different order, hence the sort.
Does anyone know of any circumstance that would cause this?
Thanks,
Julian
--
Posted via http://www.ruby-forum.com/.
Does anyone know of any circumstance that would cause this?
moulon% ruby -e 'p ["a" , 2] <=> [3, 4]'
nil
moulon%
Guy Decoux
Julian Gall wrote:
I am comparing two arrays with:
original_item_ids.sort <=> new_item_ids.sort
However, this returns nil, which seems to be against the documentation
which says the result will be -1, 0 or 1. Both arrays contain the same
values, alhough in a different order, hence the sort.Does anyone know of any circumstance that would cause this?
Improper implemented <=> method on one of the array members:
o=Object.new
=> #<Object:0x4a7c118>
def o.<=>(x) nil end
=> nil
[o] <=> [1]
=> nil
Kind regards
robert
It works for me...
% irb
irb(main):001:0> a = [1,2,3]
=> [1, 2, 3]
irb(main):002:0> b = [3,1,2]
=> [3, 1, 2]
irb(main):003:0> a.sort <=> b.sort
=> 0
Maybe you could post an irb session of your own so we could see what's happening?
--Steve
On Mar 3, 2006, at 5:37 AM, Julian Gall wrote:
I am comparing two arrays with:
original_item_ids.sort <=> new_item_ids.sort
However, this returns nil, which seems to be against the documentation
which says the result will be -1, 0 or 1. Both arrays contain the same
values, alhough in a different order, hence the sort.Does anyone know of any circumstance that would cause this?
<=> will return nil when a comparision makes no sense
eg:
irb(main):013:0> a = "a"
=> "a"
irb(main):014:0> b = 2
=> 2
irb(main):015:0> a <=> b
=> nil
On Mar 3, 2006, at 8:37 AM, Julian Gall wrote:
I am comparing two arrays with:
original_item_ids.sort <=> new_item_ids.sort
However, this returns nil, which seems to be against the documentation
which says the result will be -1, 0 or 1. Both arrays contain the same
values, alhough in a different order, hence the sort.Does anyone know of any circumstance that would cause this?
Thanks,
Julian
--
Posted via http://www.ruby-forum.com/\.
But http://www.rubycentral.com/ref/ref_c_array.html#_lt_eq_gt
"Returns an integer -1, 0, or +1 ..."
I sometimes get 0 and sometimes nil.
Julian
--
Posted via http://www.ruby-forum.com/.
Stephen Waits wrote:
Maybe you could post an irb session of your own so we could see
what's happening?
Not really possible. I am writing a Rails application with a sortable
list on a web page. An XML_Http_request serialises the ids of the list
items and POSTs them to my action controller. By the time I see this
data it is an array of identifiers (numbers) in params[:itemlist].
I extract this to a local array with:
new_item_ids =
params[:itemlist].each {|item| new_item_ids << item}
I want to compare this with another local array of my original
(unsorted) identifiers. i.e.
original_item_ids.sort <=> new_item_ids.sort
This doesn't work, although this does:
original_item_ids.sort.join('-') == new_item_ids.sort.join('-')
It is odd that join works to produce the expected string where <=>
thinks it has a problem.
Julian
--
Posted via http://www.ruby-forum.com/\.
It seems <=> is not much use if it can't be relied on to do what it
says.
I now need to compare my arrays with:
original_item_ids.sort.join('-') == new_item_ids.sort.join('-')
Which is messy.
Julian
--
Posted via http://www.ruby-forum.com/.
Based on join working this is my theory. One of the two arrays have nil's in it. nil.to_s is "" but nil <=> anything save nil is nil and will cause the comparision to fail.
On Mar 3, 2006, at 1:12 PM, Julian Gall wrote:
Stephen Waits wrote:
Maybe you could post an irb session of your own so we could see
what's happening?Not really possible. I am writing a Rails application with a sortable
list on a web page. An XML_Http_request serialises the ids of the list
items and POSTs them to my action controller. By the time I see this
data it is an array of identifiers (numbers) in params[:itemlist].I extract this to a local array with:
new_item_ids =
params[:itemlist].each {|item| new_item_ids << item}I want to compare this with another local array of my original
(unsorted) identifiers. i.e.original_item_ids.sort <=> new_item_ids.sort
This doesn't work, although this does:
original_item_ids.sort.join('-') == new_item_ids.sort.join('-')
It is odd that join works to produce the expected string where <=>
thinks it has a problem.Julian
-- Posted via http://www.ruby-forum.com/\.
Julian Gall wrote:
Stephen Waits wrote:
> Maybe you could post an irb session of your own so we could see
> what's happening?Not really possible. I am writing a Rails application with a sortable
list on a web page. An XML_Http_request serialises the ids of the list
items and POSTs them to my action controller. By the time I see this
data it is an array of identifiers (numbers) in params[:itemlist].I extract this to a local array with:
new_item_ids =
params[:itemlist].each {|item| new_item_ids << item}
new_item_ids = params[:itemlist]
I want to compare this with another local array of my original
(unsorted) identifiers. i.e.original_item_ids.sort <=> new_item_ids.sort
This doesn't work, although this does:
original_item_ids.sort.join('-') == new_item_ids.sort.join('-')
It is odd that join works to produce the expected string where <=>
thinks it has a problem.
See if this raises an error:
(original_item_ids + new_item_ids).sort
Hi --
On Fri, 3 Mar 2006, Julian Gall wrote:
It seems <=> is not much use if it can't be relied on to do what it
says.I now need to compare my arrays with:
original_item_ids.sort.join('-') == new_item_ids.sort.join('-')
Which is messy.
Can you show an example of two arrays with the same elements that give
you nil when sorted and compared with <=> ?
David
--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)
"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black
Hi --
Stephen Waits wrote:
Maybe you could post an irb session of your own so we could see
what's happening?Not really possible. I am writing a Rails application with a sortable
list on a web page. An XML_Http_request serialises the ids of the list
items and POSTs them to my action controller. By the time I see this
data it is an array of identifiers (numbers) in params[:itemlist].I extract this to a local array with:
new_item_ids =
params[:itemlist].each {|item| new_item_ids << item}I want to compare this with another local array of my original
(unsorted) identifiers. i.e.original_item_ids.sort <=> new_item_ids.sort
This doesn't work, although this does:
original_item_ids.sort.join('-') == new_item_ids.sort.join('-')
It is odd that join works to produce the expected string where <=>
thinks it has a problem.Julian
-- Posted via http://www.ruby-forum.com/\.
Based on join working this is my theory. One of the two arrays have nil's in it. nil.to_s is "" but nil <=> anything save nil is nil and will cause the comparision to fail.
However:
[1,2,nil,3].join("-")
=> "1-2--3"
so you'd get those extra -'s in one but not in the other if one but
not the other had nils.
I wonder whether the params[:itemlist] is producing strings while the
original array is integers. That would explain join working but <=>
giving up:
irb(main):009:0> ["1","2"] <=> [1,2]
=> nil
irb(main):010:0> ["1","2"].join("-") == [1,2].join("-")
=> true
David
On Sat, 4 Mar 2006, Logan Capaldo wrote:
On Mar 3, 2006, at 1:12 PM, Julian Gall wrote:
--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)
"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black
Thanks very much to Logan, David and William. David hit on the answer by
pointing out that one array has integers and the other has strings. When
I load my original id array with the values .to_s, the comparison works
as expected. Hooray! I should have realised that anything returned from
a web page would be a string.
Anyway, thanks very much, guys, for taking the time to follow this
through. I really appreciate it.
Julian
--
Posted via http://www.ruby-forum.com/.
I doubt he's displaying the result of the join when doing the comparison, it would still compare whether or not there are double dashes
On Mar 3, 2006, at 3:33 PM, dblack@wobblini.net wrote:
However:
[1,2,nil,3].join("-")
=> "1-2--3"
so you'd get those extra -'s in one but not in the other if one but
not the other had nils.
Hi --
However:
[1,2,nil,3].join("-")
=> "1-2--3"
so you'd get those extra -'s in one but not in the other if one but
not the other had nils.I doubt he's displaying the result of the join when doing the comparison, it would still compare whether or not there are double dashes
It's not a display thing; it's a <=> or == thing. If the two arrays
have unequal numbers of nils, and you join them with "-", the results
will not be equal. Actually, I realize now that since he's sorting
them, he'll never get that far anyway, because this:
[1,2,3,nil].sort
won't work at all; nor will ["1", "2", "3", nil].sort.
I'll keep my money on the theory that one array contains integers and
one contains string representations of the same integers 
David
On Sat, 4 Mar 2006, Logan Capaldo wrote:
On Mar 3, 2006, at 3:33 PM, dblack@wobblini.net wrote:
--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)
"Ruby for Rails" chapters now available
from Manning Early Access Program! Ruby for Rails
Hi --
However:
[1,2,nil,3].join("-")
=> "1-2--3"
so you'd get those extra -'s in one but not in the other if one but
not the other had nils.I doubt he's displaying the result of the join when doing the comparison, it would still compare whether or not there are double dashes
It's not a display thing; it's a <=> or == thing. If the two arrays
have unequal numbers of nils, and you join them with "-", the results
will not be equal. Actually, I realize now that since he's sorting
them, he'll never get that far anyway, because this:[1,2,3,nil].sort
won't work at all; nor will ["1", "2", "3", nil].sort.
I'll keep my money on the theory that one array contains integers and
one contains string representations of the same integersDavid
Good point.
On Mar 3, 2006, at 4:21 PM, dblack@wobblini.net wrote:
On Sat, 4 Mar 2006, Logan Capaldo wrote:
On Mar 3, 2006, at 3:33 PM, dblack@wobblini.net wrote:
--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)"Ruby for Rails" chapters now available
from Manning Early Access Program! Ruby for Rails