In mongoDb, how do you remove an array element by its index?

There is no straight way of pulling/removing by array index. In fact, this is an open issue , you may vote for it.

The workaround is using $unset and then $pull:

db.lists.update({}, {$unset : {"interests.3" : 1 }}) 
db.lists.update({}, {$pull : {"interests" : null}})

Update: as mentioned in some of the comments this approach is not atomic and can cause some race conditions if other clients read and/or write between the two operations. If we need the operation to be atomic, we could:

  • Read the document from the database
  • Update the document and remove the item in the array
  • Replace the document in the database. To ensure the document has not changed since we read it, we can use the update if current pattern described in the mongo docs

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