Re: [mongodb-user] Using distinct() with limit()

[Max Schireson]

Which 20 values would you want?

Often people want eg the most commonly occuring which means looking at everything.

Is it really just any arbitrary 20 that you need?

-- Max

On Aug 1, 2012 3:07 AM, "rang3r" <ana...@choister.net> wrote:

Hello.

Please help me with following issue.

I need to get distinct values (size of result <= n) from collection by fields.

On jira exists issue (https://jira.mongodb.org/browse/SERVER-2130) but its unresolved.

How to effectively get need values ?

Execute distinct and get first n values - dont suggest :)

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[rang3r]

Yes, i need any 10(or less) values by every field on collection.

Its debug information. 

среда, 1 августа 2012 г., 15:26:33 UTC+4 пользователь Max Schireson написал:

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[Max Schireson]

I don't know of a great solution. Part of the challenge is that you may need to look at nearly every value to get 10 distinct (imagine there are 12 possible values but 7 of them are very very rare).

If you can live with sometimes having less than 10, what I'd do in real life is just get 100 values (or 1000) and do the distinct client side, stopping if I got to 10. Not sure how fast this needs to be but you can easily dial between performance and the odds of getting all 10. While its ugly, that same basic tradeoff exists on any inindexed field even if the server supported it.

Hopefully someone else has a better idea.

-- Max

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>

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[rang3r]

So, thank you Max for yours answers.

I write following function:

function (type, coll) {

var result = {};

var filter = (type == undefined || type == null ? {} : {type:type});

var collection = (coll == undefined || coll == null ? 'objects' : coll);

db[collection].find(filter).forEach(function(object) {

for (var field_name in object) {

// var field_name = field_names[i];

var values = result[field_name];

if (values == undefined || values == null)

values = [];

if (values.length >= 10) {

continue;

}

var value = object[field_name];

if ((value != undefined || value != null) && values.indexOf(value) == -1) {

values.push(value);

result[field_name] = values;

}

}

});

return result;

}

They work as i need.

среда, 1 августа 2012 г., 20:50:33 UTC+4 пользователь Max Schireson написал:

I don't know of a great solution. Part of the challenge is that you may need to look at nearly every value to get 10 distinct (imagine there are 12 possible values but 7 of them are very very rare).

If you can live with sometimes having less than 10, what I'd do in real life is just get 100 values (or 1000) and do the distinct client side, stopping if I got to 10. Not sure how fast this needs to be but you can easily dial between performance and the odds of getting all 10. While its ugly, that same basic tradeoff exists on any inindexed field even if the server supported it.

Hopefully someone else has a better idea.

-- Max

On Aug 1, 2012 4:42 AM, "rang3r" <ana...@choister.net> wrote:
>
> Yes, i need any 10(or less) values by every field on collection.
> Its debug information. 
>
> среда, 1 августа 2012 г., 15:26:33 UTC+4 пользователь Max Schireson написал:
>>
>> Which 20 values would you want?
>>
>> Often people want eg the most commonly occuring which means looking at everything.
>>
>> Is it really just any arbitrary 20 that you need?
>>
>> -- Max
>>
>> On Aug 1, 2012 3:07 AM, "rang3r" <ana...@choister.net> wrote:
>>>
>>> Hello.
>>> Please help me with following issue.
>>> I need to get distinct values (size of result <= n) from collection by fields.
>>> On jira exists issue (https://jira.mongodb.org/browse/SERVER-2130) but its unresolved.
>>> How to effectively get need values ?
>>> Execute distinct and get first n values - dont suggest :)
>>>
>>> --
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>>> Groups "mongodb-user" group.
>>> To post to this group, send email to mongod...@googlegroups.com
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>>> mongodb-user+unsubscribe@googlegroups.com

>>> See also the IRC channel -- freenode.net#mongodb
>
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[Max Schireson]

Great! Glad its working and sorry its not built in yet...

-- Max

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