Example usage for org.apache.mahout.math.function IntIntDoubleFunction IntIntDoubleFunction

Introduction

In this page you can find the example usage for org.apache.mahout.math.function IntIntDoubleFunction IntIntDoubleFunction.

Prototype

IntIntDoubleFunction

Source Link

Usage

From source file:org.carrot2.matrix.MatrixUtils.java

License:Open Source License

/**
 * Normalizes column vectors of a sparse matrix <code>A</code> so that their L2 norm
 * (Euclidean distance) is equal to 1.0.
 * /*  w ww.  j a v  a  2  s  . c  o  m*/
 * @param A matrix to normalize
 * @param work a temporary array of <code>A.columns()</code> doubles that will be
 *            overwritten with column's original L2 norms. Supply a non-null pointer
 *            to avoid continuous allocation/freeing of memory when doing calculations
 *            in a loop. If this parameter is <code>null</code>, a new array will be
 *            allocated every time this method is called.
 * @return A with length-normalized columns (for convenience only)
 */
public static DoubleMatrix2D normalizeSparseColumnL2(final DoubleMatrix2D A, final double[] work) {
    final double[] w = prepareWork(A, work);

    A.forEachNonZero(new IntIntDoubleFunction() {
        @Override
        public double apply(int row, int column, double value) {
            w[column] += value * value;
            return value;
        }
    });

    // Take the square root
    for (int c = 0; c < A.columns(); c++) {
        w[c] = Math.sqrt(w[c]);
    }

    // Normalize
    A.forEachNonZero(new IntIntDoubleFunction() {
        @Override
        public double apply(int row, int column, double value) {
            A.setQuick(row, column, value / w[column]);
            return 0;
        }
    });

    return A;
}

---