Sparse Array Util (C#)

2017.11.9.23:09

Incremental Algorithm Implementation for sparse array utilities.

Basic Data Structure

public struct Index{public int i, j;public Index(int i, int j){this.i = i;this.j = j;}}public struct Entry{public Index ind;public double v;public Entry(int i, int j){this.ind = new Index(i,j);this.v = 0;}public Entry(int i, int j, double v):this(i,j){this.v = v;}}public struct SArray{public int m, n, num;public List<Entry> sa;public SArray(int row=10, int col=10){this.m = row;this.n = col;this.num = 0;this.sa = new List<Entry>();}public SArray(int row, int col, int number, int max):this(row, col){this.num = number;Random rd = new Random();List<Index> inds = new List<Index>();int w = 0;while(w < number){Index temp = new Index(rd.Next(number),rd.Next(number));if(inds.Contains(temp)){continue;}else{inds.Add(temp);w++;}}for(int k = 0; k<number; k++){Entry et = new Entry(inds[k].i,inds[k].j,rd.Next(max)+rd.NextDouble());sa.Add(et);}}}

Here Index struct is used to index the non-zero entry of the array; 

Entry is used to hold the index and value of the entry;

SArray is used to hold all the entries with the number of rows, columns, non-zero entries and the maximum value randomly generated. 

Attention:

1. To use generic List avoids the boxing and unboxing of ArrayList.

2. Constructor of SArray creates a list of indices first, in turn used to create entries.

Sparse Array Multiply Method

public static SArray SparseArrayMul(SArray a, SArray b){if(a.n!=b.m){WriteLine("Row number in a is NOT equal to column number in b!");}SArray result = new SArray(a.m,b.n);foreach(Entry ea in a.sa){foreach(Entry eb in b.sa){if(ea.ind.j==eb.ind.i){result.sa.Add(new Entry(ea.ind.i,eb.ind.j,ea.v*eb.v));result.num++;}}}//SparseArrayPres(result);Shrink(ref result);//SparseArrayPres(result);return result;}

Attention:

1. Idea is to multiply the necessary operands for later sum operation.

2. Has to sum up with another round of loops. 

Facilities

public static bool SparseArrayPres(SArray a){WriteLine($"SArray {a.GetHashCode()} has {a.num} entries:");WriteLine("Row\t\t Col\t\t Val");foreach(Entry e in a.sa){WriteLine($"{e.ind.i}\t\t {e.ind.j}\t\t {e.v}");}return true;}public static bool Shrink(ref SArray a){//Index ti = new Index();List<Entry> result = new List<Entry>();for(int i=0;i<a.num;i++){Entry et = a.sa[i];for(int j=i+1;j<a.num;j++){if(a.sa[i].ind.i==a.sa[j].ind.i&&a.sa[i].ind.j==a.sa[j].ind.j){et.v+=a.sa[j].v;a.num--;a.sa.RemoveAt(j);WriteLine($"Shrinked for entry ({a.sa[i].ind.i},{a.sa[i].ind.j}).");}}result.Add(et);}a.sa = result;//SparseArrayPres(a);return true;}

Attention:

1. Pres is for display.

2. Shrink is for sum the value of the result array.