Bloom Filters by Example

Bloom Filters by Example

A Bloom filter is a data structure designed to tell you, rapidly and memory-efficiently, whether an element is present in a set.

The price paid for this efficiency is that a Bloom filter is a probabilistic data structure: it tells us that the element either definitely is not in the set or may be in the set.

The base data structure of a Bloom filter is a Bit Vector. Here's a small one we'll use to demonstrate:

0	1	2	3	4	5	6	7	8	9	10	11	12	13	14

Each empty cell in that table represents a bit, and the number below it its index. To add an element to the Bloom filter, we simply hash it a few times and set the bits in the bit vector at the index of those hashes to 1.

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