io.seldon.vw.VwFeatureHash.java Source code

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Here is the source code for io.seldon.vw.VwFeatureHash.java

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/*
 * Seldon -- open source prediction engine
 * =======================================
 * Copyright 2011-2015 Seldon Technologies Ltd and Rummble Ltd (http://www.seldon.io/)
 *
 **********************************************************************************************
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at       
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 ********************************************************************************************** 
*/
package io.seldon.vw;

import org.apache.commons.lang.StringUtils;

import com.google.common.hash.HashFunction;
import com.google.common.hash.Hashing;

public class VwFeatureHash {

    final static int VW_CONSTANT_HASH = 11650396;
    final int mask;
    final int stride;

    public VwFeatureHash(int bits, int oaa) {
        mask = Math.round((float) Math.pow(2, bits) - 1);
        stride = Math.round((float) Math.pow(2, Math.ceil(log2(oaa, 2))));
        System.out.println("Stide is " + stride);
    }

    private double log2(int val, int base) {
        return Math.log(val) / Math.log(base);
    }

    private boolean isInteger(String s) {
        return isInteger(s, 10);
    }

    private boolean isInteger(String s, int radix) {
        if (s.isEmpty())
            return false;
        for (int i = 0; i < s.length(); i++) {
            if (i == 0 && s.charAt(i) == '-') {
                if (s.length() == 1)
                    return false;
                else
                    continue;
            }
            if (Character.digit(s.charAt(i), radix) < 0)
                return false;
        }
        return true;
    }

    public Integer getFeatureHash(int label, String namespace, String feature) {
        int nsHash = 0;
        if (!StringUtils.isEmpty(namespace)) {
            HashFunction h = Hashing.murmur3_32(0);
            nsHash = h.hashBytes(namespace.getBytes()).asInt();
        }
        int hcl = 0;
        if (isInteger(feature))
            hcl = Integer.parseInt(feature) + nsHash;
        else {
            HashFunction h = Hashing.murmur3_32(nsHash);
            hcl = (h.hashBytes(feature.getBytes()).asInt());
        }
        int f = ((hcl * stride) + label - 1) & mask;
        return f;
    }

    public Integer getConstantHash(int label) {
        int hash_oaa = VW_CONSTANT_HASH * stride;
        int f = (hash_oaa + label - 1) & mask;
        return f;
    }

    public static void main(String[] args) {
        VwFeatureHash hasher = new VwFeatureHash(18, 2);
        int label = 1;
        Integer hcl = hasher.getFeatureHash(label, "f", "101");
        System.out.println("code=" + hcl);
        Integer hcon = hasher.getConstantHash(label);
        System.out.println("Constant=" + hcon);
    }

}