SparseVector.java

Below is the syntax highlighted version of SparseVector.java.

```/******************************************************************************
*  Compilation:  javac SparseVector.java
*  Execution:    java SparseVector
*  Dependencies: StdOut.java
*
*  A sparse vector, implementing using a symbol table.
*
*  [Not clear we need the instance variable N except for error checking.]
*
******************************************************************************/

package edu.princeton.cs.algs4;

/**
*  The {@code SparseVector} class represents a <em>d</em>-dimensional mathematical vector.
*  Vectors are mutable: their values can be changed after they are created.
*  It includes methods for addition, subtraction,
*  dot product, scalar product, unit vector, and Euclidean norm.
*  <p>
*  The implementation is a symbol table of indices and values for which the vector
*  coordinates are nonzero. This makes it efficient when most of the vector coordindates
* are zero.
*  <p>
*  see <a href="http://algs4.cs.princeton.edu/35applications">Section 3.5</a> of
*  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*
*  @author Robert Sedgewick
*  @author Kevin Wayne
*/
public class SparseVector {
private int d;                   // dimension
private ST<Integer, Double> st;  // the vector, represented by index-value pairs

/**
* Initializes a d-dimensional zero vector.
* @param d the dimension of the vector
*/
public SparseVector(int d) {
this.d  = d;
this.st = new ST<Integer, Double>();
}

/**
* Sets the ith coordinate of this vector to the specified value.
*
* @param  i the index
* @param  value the new value
* @throws IndexOutOfBoundsException unless i is between 0 and d-1
*/
public void put(int i, double value) {
if (i < 0 || i >= d) throw new IndexOutOfBoundsException("Illegal index");
if (value == 0.0) st.delete(i);
else              st.put(i, value);
}

/**
* Returns the ith coordinate of this vector.
*
* @param  i the index
* @return the value of the ith coordinate of this vector
* @throws IndexOutOfBoundsException unless i is between 0 and d-1
*/
public double get(int i) {
if (i < 0 || i >= d) throw new IndexOutOfBoundsException("Illegal index");
if (st.contains(i)) return st.get(i);
else                return 0.0;
}

/**
* Returns the number of nonzero entries in this vector.
*
* @return the number of nonzero entries in this vector
*/
public int nnz() {
return st.size();
}

/**
* Returns the dimension of this vector.
*
* @return the dimension of this vector
* @deprecated Replaced by {@link #dimension()}.
*/
@Deprecated
public int size() {
return d;
}

/**
* Returns the dimension of this vector.
*
* @return the dimension of this vector
*/
public int dimension() {
return d;
}

/**
* Returns the inner product of this vector with the specified vector.
*
* @param  that the other vector
* @return the dot product between this vector and that vector
* @throws IllegalArgumentException if the lengths of the two vectors are not equal
*/
public double dot(SparseVector that) {
if (this.d != that.d) throw new IllegalArgumentException("Vector lengths disagree");
double sum = 0.0;

// iterate over the vector with the fewest nonzeros
if (this.st.size() <= that.st.size()) {
for (int i : this.st.keys())
if (that.st.contains(i)) sum += this.get(i) * that.get(i);
}
else  {
for (int i : that.st.keys())
if (this.st.contains(i)) sum += this.get(i) * that.get(i);
}
return sum;
}

/**
* Returns the inner product of this vector with the specified array.
*
* @param  that the array
* @return the dot product between this vector and that array
* @throws IllegalArgumentException if the dimensions of the vector and the array are not equal
*/
public double dot(double[] that) {
double sum = 0.0;
for (int i : st.keys())
sum += that[i] * this.get(i);
return sum;
}

/**
* Returns the magnitude of this vector.
* This is also known as the L2 norm or the Euclidean norm.
*
* @return the magnitude of this vector
*/
public double magnitude() {
return Math.sqrt(this.dot(this));
}

/**
* Returns the Euclidean norm of this vector.
*
* @return the Euclidean norm of this vector
* @deprecated Replaced by {@link #magnitude()}.
*/
@Deprecated
public double norm() {
return Math.sqrt(this.dot(this));
}

/**
* Returns the scalar-vector product of this vector with the specified scalar.
*
* @param  alpha the scalar
* @return the scalar-vector product of this vector with the specified scalar
*/
public SparseVector scale(double alpha) {
SparseVector c = new SparseVector(d);
for (int i : this.st.keys()) c.put(i, alpha * this.get(i));
return c;
}

/**
* Returns the sum of this vector and the specified vector.
*
* @param  that the vector to add to this vector
* @return the sum of this vector and that vector
* @throws IllegalArgumentException if the dimensions of the two vectors are not equal
*/
public SparseVector plus(SparseVector that) {
if (this.d != that.d) throw new IllegalArgumentException("Vector lengths disagree");
SparseVector c = new SparseVector(d);
for (int i : this.st.keys()) c.put(i, this.get(i));                // c = this
for (int i : that.st.keys()) c.put(i, that.get(i) + c.get(i));     // c = c + that
return c;
}

/**
* Returns a string representation of this vector.
* @return a string representation of this vector, which consists of the
*         the vector entries, separates by commas, enclosed in parentheses
*/
public String toString() {
StringBuilder s = new StringBuilder();
for (int i : st.keys()) {
s.append("(" + i + ", " + st.get(i) + ") ");
}
return s.toString();
}

/**
* Unit tests the {@code SparseVector} data type.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
SparseVector a = new SparseVector(10);
SparseVector b = new SparseVector(10);
a.put(3, 0.50);
a.put(9, 0.75);
a.put(6, 0.11);
a.put(6, 0.00);
b.put(3, 0.60);
b.put(4, 0.90);
StdOut.println("a = " + a);
StdOut.println("b = " + b);
StdOut.println("a dot b = " + a.dot(b));
StdOut.println("a + b   = " + a.plus(b));
}

}

/******************************************************************************
*  Copyright 2002-2016, Robert Sedgewick and Kevin Wayne.
*
*  This file is part of algs4.jar, which accompanies the textbook
*
*      Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
*      Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
*      http://algs4.cs.princeton.edu
*
*
*  algs4.jar is free software: you can redistribute it and/or modify
*  the Free Software Foundation, either version 3 of the License, or
*  (at your option) any later version.
*
*  algs4.jar is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  You should have received a copy of the GNU General Public License
*  along with algs4.jar.  If not, see http://www.gnu.org/licenses.
******************************************************************************/
```

Last updated: Tue May 9 03:21:46 EDT 2017.