package org.apache.mahout.math;
import org.apache.mahout.math.function.DoubleDoubleFunction;
import org.apache.mahout.math.set.OpenIntHashSet;
import java.util.Iterator;
/**
* Abstract class encapsulating different algorithms that perform the Vector operations aggregate().
* x.aggregte(y, fa, fc), for x and y Vectors and fa, fc DoubleDouble functions:
* - applies the function fc to every element in x and y, fc(xi, yi)
* - constructs a result iteratively, r0 = fc(x0, y0), ri = fc(r_{i-1}, fc(xi, yi)).
* This works essentially like a map/reduce functional combo.
*
* The names of variables, methods and classes used here follow the following conventions:
* The vector being assigned to (the left hand side) is called this or x.
* The right hand side is called that or y.
* The aggregating (reducing) function to be applied is called fa.
* The combining (mapping) function to be applied is called fc.
*
* The different algorithms take into account the different characteristics of vector classes:
* - whether the vectors support sequential iteration (isSequential())
* - what the lookup cost is (getLookupCost())
* - what the iterator advancement cost is (getIteratorAdvanceCost())
*
* The names of the actual classes (they're nested in VectorBinaryAssign) describe the used for assignment.
* The most important optimization is iterating just through the nonzeros (only possible if f(0, 0) = 0).
* There are 4 main possibilities:
* - iterating through the nonzeros of just one vector and looking up the corresponding elements in the other
* - iterating through the intersection of nonzeros (those indices where both vectors have nonzero values)
* - iterating through the union of nonzeros (those indices where at least one of the vectors has a nonzero value)
* - iterating through all the elements in some way (either through both at the same time, both one after the other,
* looking up both, looking up just one).
*
* The internal details are not important and a particular algorithm should generally not be called explicitly.
* The best one will be selected through assignBest(), which is itself called through Vector.assign().
*
* See https://docs.google.com/document/d/1g1PjUuvjyh2LBdq2_rKLIcUiDbeOORA1sCJiSsz-JVU/edit# for a more detailed
* explanation.
*/
public abstract class VectorBinaryAggregate {
public static final VectorBinaryAggregate[] OPERATIONS = {
new AggregateNonzerosIterateThisLookupThat(),
new AggregateNonzerosIterateThatLookupThis(),
new AggregateIterateIntersection(),
new AggregateIterateUnionSequential(),
new AggregateIterateUnionRandom(),
new AggregateAllIterateSequential(),
new AggregateAllIterateThisLookupThat(),
new AggregateAllIterateThatLookupThis(),
new AggregateAllLoop(),
};
/**
* Returns true iff we can use this algorithm to apply fc to x and y component-wise and aggregate the result using fa.
*/
public abstract boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc);
/**
* Estimates the cost of using this algorithm to compute the aggregation. The algorithm is assumed to be valid.
*/
public abstract double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc);
/**
* Main method that applies fc to x and y component-wise aggregating the results with fa. It returns the result of
* the aggregation.
*/
public abstract double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc);
/**
* The best operation is the least expensive valid one.
*/
public static VectorBinaryAggregate getBestOperation(Vector x, Vector y, DoubleDoubleFunction fa,
DoubleDoubleFunction fc) {
int bestOperationIndex = -1;
double bestCost = Double.POSITIVE_INFINITY;
for (int i = 0; i < OPERATIONS.length; ++i) {
if (OPERATIONS[i].isValid(x, y, fa, fc)) {
double cost = OPERATIONS[i].estimateCost(x, y, fa, fc);
if (cost < bestCost) {
bestCost = cost;
bestOperationIndex = i;
}
}
}
return OPERATIONS[bestOperationIndex];
}
/**
* This is the method that should be used when aggregating. It selects the best algorithm and applies it.
*/
public static double aggregateBest(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return getBestOperation(x, y, fa, fc).aggregate(x, y, fa, fc);
}
public static class AggregateNonzerosIterateThisLookupThat extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return fa.isLikeRightPlus() && (fa.isAssociativeAndCommutative() || x.isSequentialAccess())
&& fc.isLikeLeftMult();
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return x.getNumNondefaultElements() * x.getIteratorAdvanceCost() * y.getLookupCost();
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
Iterator<Vector.Element> xi = x.nonZeroes().iterator();
if (!xi.hasNext()) {
return 0;
}
Vector.Element xe = xi.next();
double result = fc.apply(xe.get(), y.getQuick(xe.index()));
while (xi.hasNext()) {
xe = xi.next();
result = fa.apply(result, fc.apply(xe.get(), y.getQuick(xe.index())));
}
return result;
}
}
public static class AggregateNonzerosIterateThatLookupThis extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return fa.isLikeRightPlus() && (fa.isAssociativeAndCommutative() || y.isSequentialAccess())
&& fc.isLikeRightMult();
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return y.getNumNondefaultElements() * y.getIteratorAdvanceCost() * x.getLookupCost() * x.getLookupCost();
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
Iterator<Vector.Element> yi = y.nonZeroes().iterator();
if (!yi.hasNext()) {
return 0;
}
Vector.Element ye = yi.next();
double result = fc.apply(x.getQuick(ye.index()), ye.get());
while (yi.hasNext()) {
ye = yi.next();
result = fa.apply(result, fc.apply(x.getQuick(ye.index()), ye.get()));
}
return result;
}
}
public static class AggregateIterateIntersection extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return fa.isLikeRightPlus() && fc.isLikeMult() && x.isSequentialAccess() && y.isSequentialAccess();
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return Math.min(x.getNumNondefaultElements() * x.getIteratorAdvanceCost(),
y.getNumNondefaultElements() * y.getIteratorAdvanceCost());
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
Iterator<Vector.Element> xi = x.nonZeroes().iterator();
Iterator<Vector.Element> yi = y.nonZeroes().iterator();
Vector.Element xe = null;
Vector.Element ye = null;
boolean advanceThis = true;
boolean advanceThat = true;
boolean validResult = false;
double result = 0;
while (true) {
if (advanceThis) {
if (xi.hasNext()) {
xe = xi.next();
} else {
break;
}
}
if (advanceThat) {
if (yi.hasNext()) {
ye = yi.next();
} else {
break;
}
}
if (xe.index() == ye.index()) {
double thisResult = fc.apply(xe.get(), ye.get());
if (validResult) {
result = fa.apply(result, thisResult);
} else {
result = thisResult;
validResult = true;
}
advanceThis = true;
advanceThat = true;
} else {
if (xe.index() < ye.index()) { // f(x, 0) = 0
advanceThis = true;
advanceThat = false;
} else { // f(0, y) = 0
advanceThis = false;
advanceThat = true;
}
}
}
return result;
}
}
public static class AggregateIterateUnionSequential extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return fa.isLikeRightPlus() && !fc.isDensifying()
&& x.isSequentialAccess() && y.isSequentialAccess();
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return Math.max(x.getNumNondefaultElements() * x.getIteratorAdvanceCost(),
y.getNumNondefaultElements() * y.getIteratorAdvanceCost());
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
Iterator<Vector.Element> xi = x.nonZeroes().iterator();
Iterator<Vector.Element> yi = y.nonZeroes().iterator();
Vector.Element xe = null;
Vector.Element ye = null;
boolean advanceThis = true;
boolean advanceThat = true;
boolean validResult = false;
double result = 0;
while (true) {
if (advanceThis) {
if (xi.hasNext()) {
xe = xi.next();
} else {
xe = null;
}
}
if (advanceThat) {
if (yi.hasNext()) {
ye = yi.next();
} else {
ye = null;
}
}
double thisResult;
if (xe != null && ye != null) { // both vectors have nonzero elements
if (xe.index() == ye.index()) {
thisResult = fc.apply(xe.get(), ye.get());
advanceThis = true;
advanceThat = true;
} else {
if (xe.index() < ye.index()) { // f(x, 0)
thisResult = fc.apply(xe.get(), 0);
advanceThis = true;
advanceThat = false;
} else {
thisResult = fc.apply(0, ye.get());
advanceThis = false;
advanceThat = true;
}
}
} else if (xe != null) { // just the first one still has nonzeros
thisResult = fc.apply(xe.get(), 0);
advanceThis = true;
advanceThat = false;
} else if (ye != null) { // just the second one has nonzeros
thisResult = fc.apply(0, ye.get());
advanceThis = false;
advanceThat = true;
} else { // we're done, both are empty
break;
}
if (validResult) {
result = fa.apply(result, thisResult);
} else {
result = thisResult;
validResult = true;
}
}
return result;
}
}
public static class AggregateIterateUnionRandom extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return fa.isLikeRightPlus() && !fc.isDensifying()
&& (fa.isAssociativeAndCommutative() || (x.isSequentialAccess() && y.isSequentialAccess()));
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return Math.max(x.getNumNondefaultElements() * x.getIteratorAdvanceCost() * y.getLookupCost(),
y.getNumNondefaultElements() * y.getIteratorAdvanceCost() * x.getLookupCost());
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
OpenIntHashSet visited = new OpenIntHashSet();
Iterator<Vector.Element> xi = x.nonZeroes().iterator();
boolean validResult = false;
double result = 0;
double thisResult;
while (xi.hasNext()) {
Vector.Element xe = xi.next();
thisResult = fc.apply(xe.get(), y.getQuick(xe.index()));
if (validResult) {
result = fa.apply(result, thisResult);
} else {
result = thisResult;
validResult = true;
}
visited.add(xe.index());
}
Iterator<Vector.Element> yi = y.nonZeroes().iterator();
while (yi.hasNext()) {
Vector.Element ye = yi.next();
if (!visited.contains(ye.index())) {
thisResult = fc.apply(x.getQuick(ye.index()), ye.get());
if (validResult) {
result = fa.apply(result, thisResult);
} else {
result = thisResult;
validResult = true;
}
}
}
return result;
}
}
public static class AggregateAllIterateSequential extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return x.isSequentialAccess() && y.isSequentialAccess() && !x.isDense() && !y.isDense();
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return Math.max(x.size() * x.getIteratorAdvanceCost(), y.size() * y.getIteratorAdvanceCost());
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
Iterator<Vector.Element> xi = x.all().iterator();
Iterator<Vector.Element> yi = y.all().iterator();
boolean validResult = false;
double result = 0;
while (xi.hasNext() && yi.hasNext()) {
Vector.Element xe = xi.next();
double thisResult = fc.apply(xe.get(), yi.next().get());
if (validResult) {
result = fa.apply(result, thisResult);
} else {
result = thisResult;
validResult = true;
}
}
return result;
}
}
public static class AggregateAllIterateThisLookupThat extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return (fa.isAssociativeAndCommutative() || x.isSequentialAccess())
&& !x.isDense();
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return x.size() * x.getIteratorAdvanceCost() * y.getLookupCost();
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
Iterator<Vector.Element> xi = x.all().iterator();
boolean validResult = false;
double result = 0;
while (xi.hasNext()) {
Vector.Element xe = xi.next();
double thisResult = fc.apply(xe.get(), y.getQuick(xe.index()));
if (validResult) {
result = fa.apply(result, thisResult);
} else {
result = thisResult;
validResult = true;
}
}
return result;
}
}
public static class AggregateAllIterateThatLookupThis extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return (fa.isAssociativeAndCommutative() || y.isSequentialAccess())
&& !y.isDense();
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return y.size() * y.getIteratorAdvanceCost() * x.getLookupCost();
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
Iterator<Vector.Element> yi = y.all().iterator();
boolean validResult = false;
double result = 0;
while (yi.hasNext()) {
Vector.Element ye = yi.next();
double thisResult = fc.apply(x.getQuick(ye.index()), ye.get());
if (validResult) {
result = fa.apply(result, thisResult);
} else {
result = thisResult;
validResult = true;
}
}
return result;
}
}
public static class AggregateAllLoop extends VectorBinaryAggregate {
@Override
public boolean isValid(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return true;
}
@Override
public double estimateCost(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
return x.size() * x.getLookupCost() * y.getLookupCost();
}
@Override
public double aggregate(Vector x, Vector y, DoubleDoubleFunction fa, DoubleDoubleFunction fc) {
double result = fc.apply(x.getQuick(0), y.getQuick(0));
for (int i = 1; i < x.size(); ++i) {
result = fa.apply(result, fc.apply(x.getQuick(i), y.getQuick(i)));
}
return result;
}
}
}