redimension

Redimension

Based on https://github.com/antirez/redimension

Redimension is a Redis multi-dimensional indexing and querying library implemented in order to index items in N-dimensions, and then asking for elements where each dimension is within the specified ranges.

Usage

Currently the library can index only unsigned integers of the specified precision. There are no precision limits, you can index integers composed of as much bits as you like: you specify the number of bits for each dimension in the constructor when creating a Redimension object.

An example usage in 2D is the following. Imagine you want to index persons by salary and age:

myindex = new Redimension(redis_client, "people-by-salary", 2, 64)

We created a Redimension object specifying a Redis object that must respond to the Redis commands. We specified we want 2D indexing, and 64 bits of precision for each dimension. The first argument is the key name that will represent the index as a sorted set.

Now we can add elements to our index.

myindex.index([45,120000], "Josh")
myindex.index([50,110000], "Pamela")
myindex.index([30,125000], "Angela")

The index method takes an array of integers representing the value of each dimension for the item, and an item name that will be returned when asking for ranges during the query stage.

Querying is simple. In the following query we ask for all the people with age between 40 and 50, and salary between 100000 and 115000.

myindex.query([[40,50],[100000,115000]]).then(results => {
  console.log(results) // [50, 110000, "Pamela"]
});

Ranges are always inclusive. Not a big problem since currently we can only index integers so just increment/decrement to exclude a given value.

If you want to play with the library, the above example is shipped with the source code, the file is called example1.js.

Unindexing

There are two ways in order to remove indexed data from the index. One is to specify again the coordinates and the ID, using the unindex method:

myindex.unindex([45,120000],"Josh")

However sometimes it is no longer possible to have the old data, we want just unindex or update our coordinates for a given element. In this case we may enable a feature of the library called Hash mapping. We enable it by setting a key which will represent, using an Hash type, a map between the item ID and the current indexed representation:

myindex.hashkey = "people-by-salary-map"

Once this is enabled, each time we use the index method, an hash entry will be created at the same time. We can now use two additional methods. One will simply remove an item from the index just by ID:

myindex.unindex_by_id("Josh")

The other is a variant of index that removes and re-adds the element with the updated coordinates:

myindex.update([46,120000],"Josh")

It is imporatnt to enable this feature after the object is created, and consistently for all the queries, so that the Hash and the sorted set are in sync. When this feature is enabled, to use index is not a good idea and update should be used instead regardless the added element areadly exists or not inside the index. Please refer to example2.js for an example.

Tests

npm test

License

The code is released under the BSD 2 clause license.