besides emit() in map(), can I simply omit this map-reduce cycle?

[λq]

Hi guys,

I knew that mapReduce() has a query parameter, but in my case, 

{

  'user': user1,

  'top-list': [

    {'score': score1, 'date': date1, 'app': app1},

    {'score': score4, 'date': date4, 'app': app4},

    {'score': score3, 'date': date3, 'app': app3},

  ]

}

I want to use mapReduce() to find the history position change of a particular my_app

the query parameter can do the job, but IMHO it looks redundant because when doing the map(), I have to iterate the 'top-list' array again. 

Is there something like pass() or omit() besides the standard emit() in map function? So mongodb could just skip this round of map-reduce and continue next?

[Eliot Horowitz]

I'm a bit confused by what you mean.
Is that a sample document that's in the collection?

What would the output look like?

2011/7/11 λq <lam...@gmail.com>:

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[λq]

{

  'user': user1,

  'day': '2011-07-09'

  'top-list': [

    {'score': score1, 'date': date1, 'app': app1},

    {'score': score2, 'date': date2, 'app': app2},

    {'score': score3, 'date': date3, 'app': app3},

  ]

},

{

  'user': user1,

  'day': '2011-07-10'

  'top-list': [

    {'score': score1, 'date': date1, 'app': app1},

    {'score': score3, 'date': date3, 'app': app3},

    {'score': score4, 'date': date4, 'app': app4},

  ]

},

{

  'user': user1,

  'day': '2011-07-11'

  'top-list': [

    {'score': score3, 'date': date3, 'app': app3},

    {'score': score4, 'date': date4, 'app': app4},

    {'score': score2, 'date': date2, 'app': app2},

  ]

},

Given app3, return a result like:

{'2011-07-09': 3, '2011-07-10': 2, '2011-07-11': 1}

app3 is at rank #3 place in 2011-07-09, raised to #1 and #1 in the following days.

But in the collection, app3 is out of the 'top-list'array, so I do not want the mapReduce() to process this document, yes just a 'query' parameter for mapReduce() could filter that out, but since I already need to iterate the whole 'top-list' array in the map() function, I think I don't need 'query' parameter?

So can I skip a number of documents for a map() ?

2011/7/12 Eliot Horowitz <elioth...@gmail.com>

[Eliot Horowitz]

The query would still be helpful if there are documents that don't
have app3 at all.
If all do, then the query isn't needed.

2011/7/12 λq <lam...@gmail.com>:

[λq]

Yes the 'query' parameter is helpful, but I think 'query' needs to lookup the whole 'top-list' array or index, then I look them up again because I need to find its position?

Some performance is wrong here. (I hope mongodb could just get the position of the element in the array if there is already a 'query' parameter.)

[Eliot Horowitz]

Correct - mongo won't do that for you.
You can open a feature request @ http://jira.mongodb.org

2011/7/12 λq <lam...@gmail.com>: