How to determine which number occurs most often in an array? - delphi

Question

How do I determine which value occurs the most after I filled the array with 100 random values which are between 1 and 11?

Answer 1

Here is a sample code:
procedure TForm1.Button1Click(Sender: TObject);
function Calculate: Integer;
var
Numbers: array [1..100] of Byte;
Counts: array [1..11] of Byte;
I: Byte;
begin
// Fill the array with random numbers
for I := Low(Numbers) to High(Numbers) do
Numbers[I] := Random(11) + 1;
// Count the occurencies
ZeroMemory(#Counts, SizeOf(Counts));
for I := Low(Numbers) to High(Numbers) do
Inc(Counts[Numbers[I]]);
// Identify the maximum
Result := Low(Counts);
for I := Low(Counts) + 1 to High(Counts) do
if Counts[I] > Counts[Result] then
Result := I;
end;
begin
ShowMessage(Calculate.ToString);
end;

Answer 2

It is a simple question [...]
Yes
but I can't seem to find any straight answers online.
You shouldn't be searching for solutions on-line; instead, you should start to think about how to design an algorithm able to solve the problem. For this, you may need pen and paper.
First, we need some data to work with:
const
ListLength = 100;
MinValue = 1;
MaxValue = 11;
function MakeRandomList: TArray<Integer>;
begin
SetLength(Result, ListLength);
for var i := 0 to High(Result) do
Result[i] := MinValue + Random(MaxValue - MinValue + 1);
end;
The MakeRandomList function creates a dynamic array of integers. The array contains ListLength = 100 integers ranging from MinValue = 1 to MaxValue = 11, as desired.
Now, given such a list of integers,
var L := MakeRandomList;
how do we find the most frequent value?
Well, if we were to solve this problem without a computer, using only pen and paper, we would probably count the number of times each distinct value (1, 2, ..., 11) occurs in the list, no?
Then we would only need to find the value with the greatest frequency.
For instance, given the data
2, 5, 1, 10, 1, 5, 2, 7, 8, 5
we would count to find the frequencies
X Freq
2 2
5 3
1 2
10 1
7 1
8 1
Then we read the table from the top line to the bottom line to find the row with the greatest frequency, constantly keeping track of the current winner.
Now that we know how to solve the problem, it is trivial to write a piece of code that performs this algorithm:
procedure FindMostFrequentValue(const AList: TArray<Integer>);
type
TValueAndFreq = record
Value: Integer;
Freq: Integer;
end;
var
Frequencies: TArray<TValueAndFreq>;
begin
if Length(AList) = 0 then
raise Exception.Create('List is empty.');
SetLength(Frequencies, MaxValue - MinValue + 1);
// Step 0: Label the frequency list items
for var i := 0 to High(Frequencies) do
Frequencies[i].Value := i + MinValue;
// Step 1: Obtain the frequencies
for var i := 0 to High(AList) do
begin
if not InRange(AList[i], MinValue, MaxValue) then
raise Exception.CreateFmt('Value out of range: %d', [AList[i]]);
Inc(Frequencies[AList[i] - MinValue].Freq);
end;
// Step 2: Find the winner
var Winner: TValueAndFreq;
Winner.Value := 0;
Winner.Freq := 0;
for var i := 0 to High(Frequencies) do
if Frequencies[i].Freq > Winner.Freq then
Winner := Frequencies[i];
ShowMessageFmt('The most frequent value is %d with a count of %d.',
[Winner.Value, Winner.Freq]);
end;

Answer 3

Delphi has a TDictionary class, which you can use to implement a frequency map, eg:
uses
..., System.Generics.Collections;
function MostFrequent(Arr: array of Integer) : Integer;
var
Frequencies: TDictionary<Integer, Integer>;
I, Freq, MaxFreq: Integer;
Elem: TPair<Integer, Integer>;
begin
Frequencies := TDictionary<Integer, Integer>.Create;
// Fill the dictionary with numbers
for I := Low(Arr) to High(Arr) do begin
if not Frequencies.TryGetValue(Arr[I], Freq) then Freq := 0;
Frequencies.AddOrSetValue(Arr[I], Freq + 1);
end;
// Identify the maximum
Result := 0;
MaxFreq := 0;
for Elem in Frequencies do begin
if Elem.Value > MaxFreq then begin
MaxFreq := Elem.Value;
Result := Elem.Key;
end;
end;
Frequencies.Free;
end;
var
Numbers: array [1..100] of Integer;
I: Integer;
begin
// Fill the array with random numbers
for I := Low(Numbers) to High(Numbers) do
Numbers[I] := Random(11) + 1;
// Identify the maximum
ShowMessage(IntToStr(MostFrequent(Numbers)));
end;

Answer 4

I am also still learning and therefore feel that the way I approached this problem might be a little closer to the way would have done:
procedure TForm1.GetMostOccuring;
var
arrNumbers : array[1..100] of Integer;
iNumberWithMost : Integer;
iNewAmount, iMostAmount : Integer;
I, J : Integer;
begin
for I := 1 to 100 do
arrNumbers[I] := Random(10) + 1;
iMostAmount := 0;
for I := 1 to 10 do
begin
iNewAmount := 0;
for J := 1 to 100 do
if I = arrNumbers[J] then
inc(iNewAmount);
if iNewAmount > iMostAmount then
begin
iMostAmount := iNewAmount;
iNumberWithMost := I;
end;
end;
ShowMessage(IntToStr(iNumberWithMost));
end;
I hope this is not completely useless.
It is just a simple answer to a simple question.