----- Original Message -----
From: Harper Shull <[EMAIL PROTECTED]>
> Does anyone have an algorithm (computer code)
> for calculating percentiles.
> There is a formula for doing such in Excel,
> so it must be possible to
> program. A friend is trying to write a
> macro to do such in another PC
> based software(Filemaker Pro). Thanks.
Your question is for sci.math.num-analysis.
Consult statistical a textbook about definition of
percentile. Try the following Pascal code to find K-th
smallest observation; I think that it is fast enough (or
seek in AS or TOMS).
-----------------------------
Alexander Tsyplakov
Novosibirsk State University
http://www.nsu.ru/ef/tsy/
function Selct1(K: Integer): Real;
{-- Find the K-th smallest element in an array A --}
var
I, I_Rand, I_Min, I_Max, N_Min, N_Max, N: Integer;
Q, Q_Upper, Tmp: Real;
begin
{-- The algorithm --}
N_Min := 1;
N_Max := N;
Q_Upper := 8934567; {-- Any strange number --}
while N_Min < N_Max do
begin
{-- Choose separating number Q --}
I_Rand := N_Min + Random(N_Max - N_Min + 1);
Q := A[I_Rand];
if Q = Q_Upper then
begin
I := I_Rand;
while Q = Q_Upper do
begin
I := I + 1;
if I > N_Max then I := N_Min;
if I = I_Rand then
begin
{-- All numbers are the same (= Q_Upper) --}
Selct1 := Q_Upper;
Exit;
end;
Q := A[I];
end;
end;
{-- Separate --}
I_Min := N_Min;
I_Max := N_Max;
while 1 = 1 do
begin
while (I_Min <= N_Max) and (A[I_Min] <= Q) do
Inc(I_Min);
if I_Min > N_Max then Break;
while A[I_Max] > Q do Dec(I_Max);
if I_Min > I_Max then Break;
Tmp := A[I_Min];
A[I_Min] := A[I_Max];
A[I_Max] := Tmp;
end;
Dec(I_Min);
Inc(I_Max);
if K <= I_Min then
begin
N_Max := I_Min;
Q_Upper := Q;
end
else if K >= I_Max then N_Min := I_Max;
end;
Selct1 := A[K];
end;
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