/**
* returns a matrix of LLR values from a given contingency table.
* @param contingencyTable
* @return
*/
public static double[,] GetLLRs(int[,] contingencyTable)
{
int rowNum = contingencyTable.GetLength(0);
int colNum = contingencyTable.GetLength(1);
// first get the total count of instances in the matrix
int totalCount = 0;
for (int row = 0; row < rowNum; row++)
{
for (int col = 0; col < colNum; col++)
{
totalCount += contingencyTable[row, col];
}
}
double[,] llrs = new double[rowNum, colNum];
for (int row = 0; row < rowNum; row++)
{
for (int col = 0; col < colNum; col++)
{
// get the observed value for the cell
double o = contingencyTable[row, col];
//calculate likelihood ratio
//############################################# WARNING!! CHECK THE FOLLOWING 3 LINES OF CODE
// SEE WIKIPEDIA EXAMPLE IN LIKELIHOOD RATIO
double lr = o * totalCount / DataTools.GetRowSum(contingencyTable, row) / DataTools.SumColumn(contingencyTable, col);
if (lr == 0)
{
llrs[row, col] = -999.9; // take log to get LLR
}
else
{
llrs[row, col] = Math.Log10(lr);
}
}
} // for all rows and columns
return(llrs);
}
public static double RowRelativeFrequency(int[,] table, int row, int totalCount)
{
return(DataTools.GetRowSum(table, row) / (double)totalCount);
}
