hll-stream

hll-stream

Pipe in your stream of buffers/strings to get an approximate cardinality (using HyperLogLog).

``javascript
var Hll = require('hll-stream');

var hll = new Hll(8);

//...

myDataSource.pipe(hll);

hll.on('finish', function() {
console.log(hll.cardinality());
});
`

$3

hll-stream uses 32-bit hash values since node.js won't currently do bit-wise arithmetic on more than 32 bits.

$3

#### Hll(precision, hashType, streamOpts)

Construct a new writable Hll (extends Stream.Writable).

* precision - number of bits of precision (4-16) (default 4). Memory usage is on the order of 2precision.
* hashType - which hashing algorithm to use on the values. Can be any algorithm supported by crypto.createHash (default: 'sha1').
* streamOpts - the options to pass along to the stream constructor.

#### Hll.cardinality()

Compute the approximate cardinality.

#### Hll.merge(hll)

Merge another Hll with this one. The two Hlls must have the same hashType and precision. Returns a new Hll.

* hll - another instance of hll-stream to merge with this one.

#### Hll.export()

Export the Hll's data. Returns an object like:

`javascript
{
precision: 8,
hashType: 'sha1',
registers: [...]
}
`

#### Hll.import(data)

Import Hll data (as exported by export()). Replaces any pre-existing data.

* data - the data object to import. Should be in the same format as exported by export()`.