In a mongo collection I have a list of words (millions words).
{word:'a'}
{word:'b'}
{word:'x'}
{word:'y'}
{word:'z'}
I need to get lexical adjacent of a word. I am looking for most efficient method.
Add a comment
|
1 Answer
I will suggest using two indexes.
suppose your collection name is words
db.words.ensureIndex({word: 1}) // for next word queries
db.words.ensureIndex({word: -1}) // for previous word queries
//next word query
db.words.find({word: {$gt:"a"}}).sort({word: 1}).hint({word: 1}).limit(1)
//previous word query
db.words.find({word: {$lt:"b"}}).sort({word: -1}).hint({word: -1}).limit(1)
I hope it helps
-
In your case you should use indexes with direction. Try to insert db.words.insert({word: "aa"}), and then try to look for the previous word of 'b', you will get 'a' not 'aa'.– AnasCommented Apr 1, 2013 at 12:24
-
"When creating an index, the number associated with a key specifies the direction of the index. The options are 1 (ascending) and -1 (descending). Direction doesn’t matter for single key indexes or for random access retrieval but is important if you are doing sort queries on compound indexes." docs.mongodb.org/manual/core/indexes Commented Apr 1, 2013 at 12:30
-
1