void findy(string strDataset, double y)
{
	Dataset dsY(strDataset);
	if(dsY)
	{
		int iRow = Data_list(y, &dsY);
		if(iRow == -1) 
			printf("value not found!\n");
		else
			printf("found %f at row index %d\n", dsY[iRow], iRow+1);
			// iRow+1 for row index in GUI, iRow for row index in OC
	}
	else printf("invalid dataset!\n");
}

quote:

---

The Data_list function also has a third argument to set the precision for matching the value.

---

int findmaxindex(string strDataset)
{
	Dataset dsY(strDataset);
	if(dsY)
	{
		double dMax = max(dsY);
		int iRow = Data_list(dMax, &dsY, -1);
		//Pass -1 to use Origin's default internal double comparison precision 
		//as specified by the @ND system variable
		if(iRow == -1)
			printf("Error!\n");
		else
			printf("Max value of %f found at index %d\n", dMax, iRow+1);
		return iRow;
	}
}