How to find random records in mongodb

Question

I want find many random records doing only 1 query.

I tried:

var count = db.collections.count()
var rand = function(){return Math.floor( Math.random() * count )}

db.collection.find().limit(-1).skip(rand()).next();

But this returns only one document. I need to get more random records.

How can I do this?

I have written a package https://www.npmjs.com/package/unique-random-docs that fix duplication issues and return only unique random docs npm i unique-random-docs feel free to check it out! — Detoner, Mar 01 '21 at 10:18

score 14 · Answer 1 · answered Dec 26 '13 at 05:54

14

Another way to achive

db.Colletion.find().limit( 50 ).skip( _rand() * db.Collection.count() )

change the limit() as per your requirement, Hope this will Help....

Thanks

answered Dec 26 '13 at 05:54

nish71

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This too inefficient. Getting all records first, then offsetting cannot be the right way for this... – danielrvt Jun 04 '15 at 22:47
This is fine, but if I want a PHP code to get the random records out of 100 records and display how that would look like? – Puneeth Feb 15 '16 at 06:32
`db.COLLECTION.find().limit( 1 ).skip(_rand() * db.COLLECTION.count())` – awesome for me, thanks! – dimpiax Nov 09 '16 at 00:24
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@danielrvt, you're wrong since MongoDB uses cursors, this will work just fine. – Sercan Ozdemir May 20 '17 at 13:06

score 4 · Answer 2 · answered Dec 25 '13 at 14:18

4

Pass a function that returns a Boolean value in the find parameter:

db.collection.find(function () {return Boolean(Math.floor(Math.random() * 2))})

You can see how many records were returned using count():

db.collection.find(...).count()

Also, if you want to limit the document cout use limit():

db.collection.find(...).limit(/* how many? */)

answered Dec 25 '13 at 14:18

Ionică Bizău

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Of course the speed of such a thing means you should never do this – Sammaye Dec 25 '13 at 20:21
@Sammaye I know it's not optimal, but for Mongo shell it's enough. – Ionică Bizău Dec 26 '13 at 06:18
please give me code for PHP – Ruben Yeghikyan Dec 26 '13 at 14:29
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When using `limit`, this is going to strongly favor docs near the beginning of the collection. – JohnnyHK Dec 07 '14 at 23:35

How to find random records in mongodb

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