Determine the number of unique values ​​in an array

Question

I am looking for an effective way to determine the number of unique values ​​in an array.

My current approach:

• Fast array of integer arrays
• Then run a loop to compare the elements.

In code:

  yearHolder := '';
  for I := 0 to  High(yearArray) do
  begin
    currYear := yearArray[i];
    if (yearHolder <> currYear) then
    begin
      yearHolder := currYear;
      Inc(uniqueYearNumber);
    end;
  end;

Answer 1

Here is an example with THashedStringList:

hl := THashedStringList.Create; // in Inifiles
try
  hl.Sorted := True;
  hl.Duplicates := dupIgnore; // ignores attempts to add duplicates
  for i := 0 to  High(yearArray) do
    hl.Add(yearArray[i]);
  uniqueYearCount := hl.Count;
finally
  hl.Free;
end;

Answer 2

In general, you can use this algorithm:

• Create a hash table that maps the year to the number of occurrences.
• For each number in your array, put the corresponding entry in the hash table.
• When done, get the number of entries in the hash.

"". , , . , 0-3000 . , - . 0s. , 2009 , arr [2009]. arr [i] >= 1.

Answer 3

: .

D2009 THashedStringList ( → ), D2009, . .

Answer 4

Delphi, DeHL, : uniqueWidgets: = List.Create(MassiveListOfNonUniqueWidgets.Distinct());

:

Answer 5

Set , , Set. , Java, DDL,.Net ( ), , .

Answer 6

A more efficient algorithm would be to dump the entire hash table (not sure if Delphi even has this).

• Go through the list (in this case yearArray) and use the values ​​as keys in the hash table.
• Get the number of keys in a hash table.