Bloom filters can very quickly answer variations on the Yes/No question “is this item in the set?”, like “have I seen this item before?”
While bloom filters can give false positives, they cannot give false negatives. When
// NPM
npm install --save @polkajs/bloom-filter
// YARN
yarn add @polkajs/bloom-filterconst Bloom = require('@polkajs/bloom-filter').default;
let bloom = new Bloom(16, 8); // 16 byte length, assuming max 8 inputs
B.add("cat");
B.add("parrot");
B.add("monkey");
console.log(B);
// Bloom {
// bitmapBits: 128,
// k: 2,
// bitmap: <Buffer 00 00 80 00 00 00 08 00 00 20 01 00 88 00 00 00>,
// numHashes: 8,
// hashFunc: [Function]
// }
let dog = B.inSet("dog");
let cat = B.inSet("cat");
console.log("is 'dog' in the set?", dog);
// false
console.log("is 'cat' in the set?", cat);
// true
console.log(B.toString());
// 00008000000008000020010088000000create a new bloom
new Bloom(size: number, numHashes: number, hashFunc?: Function)
- size: number of bytes in bloom map
- numHashes: max number of inputs
- hashFun: [OPTIONAL] replace the murmurhash3 algorithm
add a new input
bloom.add(data: string)
- data: input string to be mapped
check if a value exists in the bloom filter set
bloom.inset(data: string): bool
- data: input string to be checked
hexadecimal string of the current mapping of inputs
bloom.toString(): string
takes
bloom.extendBloom(b: Bloom): Bloom
- b bloom filter to extend from
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