How to calculate Hemming Distance in CosmosDB?

Question

Each item in my collection has a 64-bit number, which represents dhash of the image. I want to run a query by this field, which will return all items, that have Hamming Distance more or less than some param.

In MySQL I would use BIT_COUNT function. Is there any built-in analog of it in CosmosDB? If no, then how my HAMMING_DISTANCE UDF should look like since JS doesn't support bitwise operations on 64-bit numbers?

Answer 1

To solve this I took code from long.js and ImageHash for using in CosmosDB UDF. All cudos to their authors.

See gist it here https://gist.github.com/okolobaxa/55cc08a0d67bc60505bfe3ab4f8bc33c

Usage:

SELECT udf.HAMMING_DISTANCE(files.ContentId, '1279796919517872320') FROM files

But please note a few things:

1. CosmosDB doesn't support 64-bit numbers as numbers, you have to store them as strings.
2. Using this UDF costs a lot of RUs

I created a feature request on the CosmosDB Feedback forum to add built-in support of such functions. Please vote for these ideas if you're interested in it too:

• Built-in functions for bitwise operations

• Built-in functions for calculating distance metrics