Re: [MongoMapper] Sorting collections by arrays?

[Brian Hempel]

If your result set is small, you can sort it in Ruby.

The reason Mongo sorts that way is because of how its indexes are implemented. The indexes probably look like...

== my_docs.animal ==

armadillo -> doc2

cat -> doc5

dog -> doc5

zebra -> doc2

…w/no information about array position. Based on the docs, it looks like this is your only option for Array indexing…

http://www.mongodb.org/display/DOCS/Multikeys

…but the Mongo list might give you better advice.

Brian

On Jun 22, 2012, at 5:21 PM, Seth Boyles wrote:

I have a collection I want to sort by an array attribute.  However I want this sorted lexically by each element of the array.  For example, ["dog, "cat"] should be sorted in front of  ["zebra", "armadillo"] because the first element of the first array "dog" is head of the first element of the second array.  However this is not how mongomapper or mongodb does this--instead the ["z","a"] array comes first because the second element "armadillo" is before all the other elements in the first array--and I was wondering if anyone knew if mongo or mongomapper had any way of supporting this type of lexical sort.

Thanks,

Seth

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[Justin Dossey]

I would be tempted to implement a merge sort using map/reduce.  It might not meet your needs, but it would be fun to code up!

Justin Dossey

[Jon Kern]

if your result set is not small, you can add a callback to update a
special column you can then use reliably for sorting...

jon

blog: http://technicaldebt.com
twitter: http://twitter.com/JonKernPA

Brian Hempel said the following on 6/22/12 5:56 PM:

> If your result set is small, you can sort it in Ruby.
>
> The reason Mongo sorts that way is because of how its indexes are
> implemented. The indexes probably look like...
>
> == my_docs.animal ==
> armadillo -> doc2
> cat -> doc5
> dog -> doc5
> zebra -> doc2
>

> �w/no information about array position. Based on the docs, it looks
> like this is your only option for Array indexing�
>
> http://www.mongodb.org/display/DOCS/Multikeys
>
> �but the Mongo list might give you better advice.