/// <summary>
/// returns quartiles (0th, 1st, 2nd, 3rd, 4th, 5th.)
///
/// see: https://en.wikipedia.org/wiki/Quantile#Examples
///
/// This generic overload returns discrete values: the items at those quartile indicies rounded down. (no averaging of values)
/// the float based overload will average results.
/// </summary>
static public Quartiles <T> ComputeQuartiles <T>(Span <T> afVal, int length)
{
int iSize = length;
int iMid = iSize / 2; //this is the mid from a zero based index, eg mid of 7 = 3;
var toReturn = new Quartiles <T>();
toReturn.count = length;
//q0 and q4
toReturn.q0 = afVal[0];
toReturn.q4 = afVal[length - 1];
toReturn.q2 = afVal[iMid];
int iMidMid = iMid / 2;
toReturn.q1 = afVal[iMidMid];
toReturn.q3 = afVal[iMid + iMidMid];
return(toReturn);
}
/// <summary>
/// returns quartiles (0th, 1st, 2nd, 3rd, 4th, 5th.)
///
/// see: https://en.wikipedia.org/wiki/Quantile#Examples
///
/// Return the quartile values of an ordered set of doubles
/// assume the sorting has already been done.
///
/// This actually turns out to be a bit of a PITA, because there is no universal agreement
/// on choosing the quartile values. In the case of odd values, some count the median value
/// in finding the 1st and 3rd quartile and some discard the median value.
/// the two different methods result in two different answers.
/// The below method produces the arithmatic mean of the two methods, and insures the median
/// is given it's correct weight so that the median changes as smoothly as possible as
/// more data ppints are added.
///
/// This method uses the following logic:
///
/// ===If there are an even number of data points:
/// Use the median to divide the ordered data set into two halves.
/// The lower quartile value is the median of the lower half of the data.
/// The upper quartile value is the median of the upper half of the data.
///
/// ===If there are (4n+1) data points:
/// The lower quartile is 25% of the nth data value plus 75% of the (n+1)th data value.
/// The upper quartile is 75% of the (3n+1)th data point plus 25% of the (3n+2)th data point.
///
///===If there are (4n+3) data points:
/// The lower quartile is 75% of the (n+1)th data value plus 25% of the (n+2)th data value.
/// The upper quartile is 25% of the (3n+2)th data point plus 75% of the (3n+3)th data point.
///
/// </summary>
static public Quartiles <float> ComputeQuartiles(Span <float> afVal, int length)
{
int iSize = length;
int iMid = iSize / 2; //this is the mid from a zero based index, eg mid of 7 = 3;
var toReturn = new Quartiles <float>();
toReturn.count = length;
//q0 and q4
toReturn.q0 = afVal[0];
toReturn.q4 = afVal[length - 1];
if (iSize % 2 == 0)
{
//================ EVEN NUMBER OF POINTS: =====================
//even between low and high point
toReturn.q2 = (afVal[iMid - 1] + afVal[iMid]) / 2;
int iMidMid = iMid / 2;
//easy split
if (iMid % 2 == 0)
{
toReturn.q1 = (afVal[iMidMid - 1] + afVal[iMidMid]) / 2;
toReturn.q3 = (afVal[iMid + iMidMid - 1] + afVal[iMid + iMidMid]) / 2;
}
else
{
toReturn.q1 = afVal[iMidMid];
toReturn.q3 = afVal[iMidMid + iMid];
}
}
else if (iSize == 1)
{
//================= special case, sorry ================
toReturn.q1 = afVal[0];
toReturn.q2 = afVal[0];
toReturn.q3 = afVal[0];
}
else
{
//odd number so the median is just the midpoint in the array.
toReturn.q2 = afVal[iMid];
if ((iSize - 1) % 4 == 0)
{
//======================(4n-1) POINTS =========================
int n = (iSize - 1) / 4;
toReturn.q1 = (afVal[n - 1] * .25f) + (afVal[n] * .75f);
toReturn.q3 = (afVal[3 * n] * .75f) + (afVal[3 * n + 1] * .25f);
}
else if ((iSize - 3) % 4 == 0)
{
//======================(4n-3) POINTS =========================
int n = (iSize - 3) / 4;
toReturn.q1 = (afVal[n] * .75f) + (afVal[n + 1] * .25f);
toReturn.q3 = (afVal[3 * n + 1] * .25f) + (afVal[3 * n + 2] * .75f);
}
}
return(toReturn);
}
protected override string _QuartileToString(Quartiles <TimeSpan> hist)
{
return($"{name} Quantiles: {hist.q0.TotalMilliseconds.ToString("F1") } / {hist.q1.TotalMilliseconds.ToString("F1") } / {hist.q2.TotalMilliseconds.ToString("F1") } / {hist.q3.TotalMilliseconds.ToString("F1") } / {hist.q4.TotalMilliseconds.ToString("F1") } ({hist.count} samples)");
}
