Fast and concise bitvectors, based on Lemur Project.
npm install node-ewahSimple, fast bitmap vectors ( sparse and dense ) and indices implementation, based on Lemur project: (http://code.google.com/p/lemurbitmapindex/)
Features:
* Allows Javascript code to generate and manipulate EWAH encoded bitvectors of arbitrary length
* Word-aligned compression scheme facilitates fast encoding/decoding while retaining pretty small memory footprint
* Really speedy, thanks to the C++ background, that was wrapped to be usable in JS using some dark V8 magic :-)
* Mostly drop-in syntactic replacement for Array ( where possible and makes sense )
* Support (de)serialization of encoded bitmaps
* Well-commented and clean code
Install it in node.js ( npm support is upcoming ):
``
Clone repository:
git clone git@github.com:olddaos/node-ewah.git
Assemble using WAF:
node-waf configure build
All done...
`
`javascript`
var BitVector = require('node-ewah');
Then create some vectors ...
`javascript
var vGoods = new BitVector();
var vSpecies = new BitVector();
// This is the bitvector of docids, that contain the word "goods". Bit number #xxx is on, if and only if document number #xxx contains word "goods".
vGoods.push(10);
vGoods.push(1234);
vGoods.push(101234);
// This is the bitvector of docids, that contain the word "species". Bit is the for the same reason.
vSpecies.push(1234);
vSpecies.push(1239);
vSpecies.push(10000);
// Now lets know, what documents contains first or second term
// This operation is performed using native machine words, that contain bitmap fragments, and so is extremely fast
var vMergedVector = vGoods.rawor( vSpecies );
// Check, that things are retrieved fine...
var checkVector = vGoods.map( function(x) { console.log( "From bitvector vGoods: " + x ); } );
// Check merging result...
var checkMerged = vMergedVector.map( function(x) { console.log( "From bitvector vMerged: " + x ); } );
`
Appends bit_id to the bitmap. Sorry, no random access today, but is developed hard...
This thing is the same as in plain vanilla Array
Applies logical OR operation on This and vectorRight vectors. Result is new vector or undef if things were wrong.
Does not account for sparsity ( see. sparseor for that ), thus it could be slower, when applied to sparse vectors
Applies logical AND operation on This and vectorRight vectors. Result is new vector or undef if things were wrong
Returns the number of nonzero bits ( population count ). Such a long name is to avoid confusion with pop ( which is Array-specific method )
Returns compressed size ( IN BITS! ).
In node.js
```
> node ewah.js
Requires node.js
v.1.0 was released