How to alpha sort a stringgrid on a form on a given column in Delphi?
There's no built in sort facility for TStringGrid, so you need to roll your own. Personally, I use some general purpose sorting code that can sort anything provided a compare function and an exchange function:
type
TCompareIndicesFunction = function(Index1, Index2: Integer): Integer of object;
TExchangeIndicesProcedure = procedure(Index1, Index2: Integer) of object;
procedure Sort(const First, Last: Integer; Compare: TCompareIndicesFunction; Exchange: TExchangeIndicesProcedure);
begin
//insert search algorithm here
end;
You could look at how Generics.Collections.TArray.Quicksort is implemented to see how to fill in the missing code above.
The essential point is that your Compare and Exchange functions, which are methods of objects, contain the knowledge of how to compare items in the string grid, and then how to swap them.
Related
In Delphi, I declared a 3x3 matrix table as an array of array of Single, like this:
m_Table: array [0..2] of array [0..2] of Single;
Now I want to memory compare the content with another table, or memory copy the table content from another table. I know that I can create a nested loop to do that, but I want to do the job without any loop, if possible.
My question is, it is correct to copy or compare the memory like this:
CompareMem(m_Table, other.m_Table, 9 * SizeOf(Single));
CopyMemory(m_Table, other.m_Table, 9 * SizeOf(Single));
If not, what is the correct way to do that?
And as a subsidiary question, is there a better way to get the length to copy instead of 9 * SizeOf(Single), like e.g. SizeOf(m_Table^)?
Regards
The code in the question works fine. Personally I would say that Move is the idiomatic way to copy memory. Further I would use SizeOf(m_Table) to obtain the size of the type.
I would point out that your comparison differs from the floating point equality operator. Perhaps that's what you want, but you should be aware of this. For instance zero and minus zero compare equal using floating point comparison but not with memory compare. And NaNs always compare not equal, even with identical bit patterns.
Let me also comment that it would make your code more extendible if you declared a type for these matrices. Without that you won't be able to write functions that accept such objects.
The correct and easiest way may be to define a type:
type
TMatrix3x3 = array [0..2,0..2] of Single;
Then you can directly write:
var
v1, v2: TMatrix3x3;
begin
fillchar(v1,sizeof(v1),0);
move(v1,v2,sizeof(v1));
if comparemem(#v1,#v2,sizeof(v1)) then
writeln('equals');
end;
Using sizeof() make your code safe and readable.
You may define a wrapper type with methods:
{ TMatrix3x3 }
type
TMatrix3x3 = record
v: array [0..2,0..2] of Single;
procedure Zero;
procedure Copy(var dest: TMatrix3x3);
procedure Fill(const source: TMatrix3x3);
function Equals(const other: TMatrix3x3): boolean;
end;
procedure TMatrix3x3.Copy(var dest: TMatrix3x3);
begin
move(v,dest,sizeof(v));
end;
function TMatrix3x3.Equals(const other: TMatrix3x3): boolean;
begin
result := CompareMem(#v,#other.v,sizeof(v));
end;
procedure TMatrix3x3.Fill(const source: TMatrix3x3);
begin
move(source,v,sizeof(v));
end;
procedure TMatrix3x3.Zero;
begin
fillchar(v,sizeof(v),0);
end;
Including then advanced features like implicit assignment, and operators, if needed.
But don't reinvent the wheel, if you really to work with matrix arithmetic. Use an already existing and fully tested library, which will save you a lot of trouble and debugging time.
You should use standard TMatrix type from System.Math.Vectors unit, then you can just compare it directly as if Matrix1 = Matrix2 then and assign as Matrix1 := Matrix2
I want to write a procedure that appends to an array of Integer, but Delphi IDE gives me compile-time error 'Incompatyble types'. This is my code :
procedure appendToIntegerArray(var intArr : array of Integer; valueToAppend : Integer);
var
counter : Integer;
begin
counter := Length(intArr);
SetLength(intArr, counter + 1); // This is where it gives me the compile-time error
intArr[counter] := valueToAppend;
end;
Can anyone help me fix my procedure ?
You are facing the error because SetLength operates on dynamic arrays and that is not a dynamic array. That is an open array parameter.
You'll need to use a dynamic array instead:
procedure appendToIntegerArray(var intArr: TArray<Integer>; valueToAppend: Integer);
....
If you use an older Delphi that does not support generic arrays, you'll need to declare a type for the array:
type
TIntegerArray = array of Integer;
procedure appendToIntegerArray(var intArr: TIntegerArray; valueToAppend: Integer);
....
Or you could use the type declared in the RTL, TIntegerDynArray. This type is declared in the Types unit.
One of the irritations of Delphi's type system is that a type like TIntegerArray is not assignment compatible with, say, TIntegerDynArray because they are distinct types. That makes it harder than it should be to work with code that uses distinct array types. One of the great benefits of generic arrays is that the rules for type compatibility of generics are a little more forgiving. So, if you can use TArray<T>, do so.
If you are appending item by item, then I would generally suggest that a list class would be better. In this case you would use TList<Integer> and simply call its Add method.
It's one of the quirks of Delphi's syntax: declaring an array of whatever as a function parameter does not define it as an array like you might think, but as an open array, a "magic" type that can accept any array of the correct base type. If you want to use a specific type of array, you need a named type.
This is the sort of thing that the generic TArray<T> was designed for. Make your parameter a TArray<integer> if you can. If not, consider updating to a newer version of Delphi (you're missing out on a whole lot if you're still on an older version!) and in the meantime, declare an array type like so:
type
TMyIntegerArray = array of integer;
And use that type as your parameter type, rather than declaring array of integer there.
Just a little question, I'm not finding a specific answer so i guessed it might be faster to ask here.
The compiler rejects the code below with the following error:
incompatible types 'dynamic array' and 'array of string'
TMailInfo = record
FileName,
MailAdresse,
MailBCC,
MailCC,
MailBetreff: string;
MailText,
Anhang: array of string;
MailAcknowledge,
MailTXT: Boolean
end;
class function TEMail.SendOutlookCOMMail(aFileName, aMailAdresse,
aMailBCC, aMailCC, aMailBetreff: string;
aMailText, aAnhang: array of string;
const aMailAcknowledge, aMailTXT: Boolean): Boolean;
var
mailInfo: TMailInfo;
begin
...
mailInfo.MailBetreff := aMailBetreff; // these two lines cause the error
mailInfo.MailText := aMailText;
...
end;
What am I doing wrong? Both are arrays of string, so I don't get why one seems to be dynamic.
You cannot readily assign to MailText and Anhang because you cannot declare another object with a compatible type. That's because you used a dynamic array type inline in your record declaration. You really need to use a type that can be named. To illustrate a bit better, consider this:
X: array of Integer;
Y: array of Integer;
Now X and Y are of different types and X := Y does not compile.
The other problem is your open array parameter. An open array parameter is assignment compatible with nothing. You can copy element by element, but you cannot assign the array in one go.
The best way out of this is to declare the field like this:
MailText,
Anhang: TArray<string>;
And change the open array parameters in the function to also be of that type.
Then you need to decide whether you want to copy the reference or the array:
MailText := aMailText; // copy reference, or
MailText := Copy(aMailText); // copy array
You have two problems. First, as David says, two declarations of a type that look the same, but are declared separately, make them different, assignment incompatible types.
Weirdly enough, this is not so for generic types, like TArray<string>, so it makes sense to use that, if you version of Delphi supports it.
But the second problem is that you are confusing an open array parameter like aMailText with a dynamic array like mailInfo.MailText. aMailText, the parameter, is not necessarily a dynamic array at all, it can be any kind of array.
Take a look at the documentation: Open Arrays
Another explanation: Open array parameters and array of const
Consider the following record:
TMyRecord = record
b: Boolean;
// 3 bytes of padding in here with default record alignment settings
i: Integer;
end;
I wish to implement IEqualityComparer<TMyRecord>. In order to do so I want to call TEqualityComparer<TMyRecord>.Construct. This needs to be supplied with a TEqualityComparison<TMyRecord> which presents no problems to me.
However, Construct also requires a THasher<TMyRecord> and I would like to know the canonical method for implementing that. The function needs to have the following form:
function MyRecordHasher(const Value: TMyRecord): Integer;
begin
Result := ???
end;
I expect that I need to call BobJenkinsHash on both fields of the record value and then combine them some how. Is this the right approach, and how should I combine them?
The reason I don't use TEqualityComparison<TMyRecord>.Default is that it uses CompareMem and so will be incorrect due to the record's padding.
The Effective Java (by Joshua Bloch) section about overriding hashCode could be useful. It shows how the individual parts of the object (or record) can be combined to efficiently construct a hashCode.
A good hash function tends to produce unequal hash codes for unequal
objects. This is exactly what is meant by the third provision of the
hashCode contract. Ideally, a hash function should distribute any
reasonable collection of unequal instances uniformly across all
possible hash values. Achieving this ideal can be extremely difficult.
Luckily it is not too difficult to achieve a fair approximation. Here
is a simple recipe:
Store some constant nonzero value, say 17, in an int variable called result.
For each significant field f in your object (each field taken into account by the equals method, that is), do the following:
a. Compute an int hash code c for the field: ..... details omitted ....
b. Combine the hash code c computed in step a into
result as follows: result = 37*result + c;
Return result.
When you are done writing the hashCode method, ask yourself whether equal instances have equal hash codes. If not, figure out why
and fix the problem.
This can be translated into Delphi code as follows:
{$IFOPT Q+}
{$DEFINE OverflowChecksEnabled}
{$Q-}
{$ENDIF}
function CombinedHash(const Values: array of Integer): Integer;
var
Value: Integer;
begin
Result := 17;
for Value in Values do begin
Result := Result*37 + Value;
end;
end;
{$IFDEF OverflowChecksEnabled}
{$Q+}
{$ENDIF}
This then allows the implementation of MyRecordHasher:
function MyRecordHasher(const Value: TMyRecord): Integer;
begin
Result := CombinedHash([IfThen(Value.b, 0, 1), Value.i]);
end;
Say I have an array of records which I want to sort based on one of the fields in the record. What's the best way to achieve this?
TExample = record
SortOrder : integer;
SomethingElse : string;
end;
var SomeVar : array of TExample;
You can add pointers to the elements of the array to a TList, then call TList.Sort with a comparison function, and finally create a new array and copy the values out of the TList in the desired order.
However, if you're using the next version, D2009, there is a new collections library which can sort arrays. It takes an optional IComparer<TExample> implementation for custom sorting orders. Here it is in action for your specific case:
TArray.Sort<TExample>(SomeVar , TDelegatedComparer<TExample>.Construct(
function(const Left, Right: TExample): Integer
begin
Result := TComparer<Integer>.Default.Compare(Left.SortOrder, Right.SortOrder);
end));
(I know this is a year later, but still useful stuff.)
Skamradt's suggestion to pad integer values assumes you are going to sort using a string compare. This would be slow. Calling format() for each insert, slower still. Instead, you want to do an integer compare.
You start with a record type:
TExample = record
SortOrder : integer;
SomethingElse : string;
end;
You didn't state how the records were stored, or how you wanted to access them once sorted. So let's assume you put them in a Dynamic Array:
var MyDA: Array of TExample;
...
SetLength(MyDA,NewSize); //allocate memory for the dynamic array
for i:=0 to NewSize-1 do begin //fill the array with records
MyDA[i].SortOrder := SomeInteger;
MyDA[i].SomethingElse := SomeString;
end;
Now you want to sort this array by the integer value SortOrder. If what you want out is a TStringList (so you can use the ts.Find method) then you should add each string to the list and add the SortOrder as a pointer. Then sort on the pointer:
var tsExamples: TStringList; //declare it somewhere (global or local)
...
tsExamples := tStringList.create; //allocate it somewhere (and free it later!)
...
tsExamples.Clear; //now let's use it
tsExamples.sorted := False; //don't want to sort after every add
tsExamples.Capacity := High(MyDA)+1; //don't want to increase size with every add
//an empty dynamic array has High() = -1
for i:=0 to High(MyDA) do begin
tsExamples.AddObject(MyDA[i].SomethingElse,TObject(MyDA[i].SortOrder));
end;
Note the trick of casting the Integer SortOrder into a TObject pointer, which is stored in the TStringList.Object property. (This depends upon the fact that Integer and Pointer are the same size.) Somewhere we must define a function to compare the TObject pointers:
function CompareObjects(ts:tStringList; Item1,Item2: integer): Integer;
begin
Result := CompareValue(Integer(ts.Objects[Item1]), Integer(ts.Objects[Item2]))
end;
Now, we can sort the tsList on .Object by calling .CustomSort instead of .Sort (which would sort on the string value.)
tsExamples.CustomSort(#CompareObjects); //Sort the list
The TStringList is now sorted, so you can iterate over it from 0 to .Count-1 and read the strings in sorted order.
But suppose you didn't want a TStringList, just an array in sorted order. Or the records contain more data than just the one string in this example, and your sort order is more complex. You can skip the step of adding every string, and just add the array index as Items in a TList. Do everything above the same way, except use a TList instead of TStringList:
var Mlist: TList; //a list of Pointers
...
for i:=0 to High(MyDA) do
Mlist.add(Pointer(i)); //cast the array index as a Pointer
Mlist.Sort(#CompareRecords); //using the compare function below
function CompareRecords(Item1, Item2: Integer): Integer;
var i,j: integer;
begin
i := integer(item1); //recover the index into MyDA
j := integer(item2); // and use it to access any field
Result := SomeFunctionOf(MyDA[i].SomeField) - SomeFunctionOf(MyDA[j].SomeField);
end;
Now that Mlist is sorted, use it as a lookup table to access the array in sorted order:
for i:=0 to Mlist.Count-1 do begin
Something := MyDA[integer(Mlist[i])].SomeField;
end;
As i iterates over the TList, we get back the array indexes in sorted order. We just need to cast them back to integers, since the TList thinks they're pointers.
I like doing it this way, but you could also put real pointers to array elements in the TList by adding the Address of the array element instead of it's index. Then to use them you would cast them as pointers to TExample records. This is what Barry Kelly and CoolMagic said to do in their answers.
If your need sorted by string then use sorted TStringList and
add record by TString.AddObject(string, Pointer(int_val)).
But If need sort by integer field and string - use TObjectList and after adding all records call TObjectList.Sort with necessary sorted functions as parameter.
This all depends on the number of records you are sorting. If you are only sorting less than a few hundred then the other sort methods work fine, if you are going to be sorting more, then take a good look at the old trusty Turbo Power SysTools project. There is a very good sort algorithm included in the source. One that does a very good job sorting millions of records in a efficient manner.
If you are going to use the tStringList method of sorting a list of records, make sure that your integer is padded to the right before inserting it into the list. You can use the format('%.10d',[rec.sortorder]) to right align to 10 digits for example.
The quicksort algorithm is often used when fast sorting is required. Delphi is (Or was) using it for List.Sort for example.
Delphi List can be used to sort anything, but it is an heavyweight container, which is supposed to look like an array of pointers on structures. It is heavyweight even if we use tricks like Guy Gordon in this thread (Putting index or anything in place of pointers, or putting directly values if they are smaller than 32 bits): we need to construct a list and so on...
Consequently, an alternative to easily and fastly sort an array of struct might be to use qsort C runtime function from msvcrt.dll.
Here is a declaration that might be good (Warning: code portable on windows only).
type TComparatorFunction = function(lpItem1: Pointer; lpItem2: Pointer): Integer; cdecl;
procedure qsort(base: Pointer; num: Cardinal; size: Cardinal; lpComparatorFunction: TComparatorFunction) cdecl; external 'msvcrt.dll';
Full example here.
Notice that directly sorting the array of records can be slow if the records are big. In that case, sorting an array of pointer to the records can be faster (Somehow like List approach).
With an array, I'd use either quicksort or possibly heapsort, and just change the comparison to use TExample.SortOrder, the swap part is still going to just act on the array and swap pointers. If the array is very large then you may want a linked list structure if there's a lot of insertion and deletion.
C based routines, there are several here
http://www.yendor.com/programming/sort/
Another site, but has pascal source
http://www.dcc.uchile.cl/~rbaeza/handbook/sort_a.html
Use one of the sort alorithms propose by Wikipedia. The Swap function should swap array elements using a temporary variable of the same type as the array elements. Use a stable sort if you want entries with the same SortOrder integer value to stay in the order they were in the first place.
TStringList have efficient Sort Method.
If you want Sort use a TStringList object with Sorted property to True.
NOTE: For more speed, add objects in a not Sorted TStringList and at the end change the property to True.
NOTE: For sort by integer Field, convert to String.
NOTE: If there are duplicate values, this method not is Valid.
Regards.
If you have Delphi XE2 or newer, you can try:
var
someVar: array of TExample;
list: TList<TExample>;
sortedVar: array of TExample;
begin
list := TList<TExample>.Create(someVar);
try
list.Sort;
sortedVar := list.ToArray;
finally
list.Free;
end;
end;
I created a very simple example that works correctly if the sort field is a string.
Type
THuman = Class
Public
Name: String;
Age: Byte;
Constructor Create(Name: String; Age: Integer);
End;
Constructor THuman.Create(Name: String; Age: Integer);
Begin
Self.Name:= Name;
Self.Age:= Age;
End;
Procedure Test();
Var
Human: THuman;
Humans: Array Of THuman;
List: TStringList;
Begin
SetLength(Humans, 3);
Humans[0]:= THuman.Create('David', 41);
Humans[1]:= THuman.Create('Brian', 50);
Humans[2]:= THuman.Create('Alex', 20);
List:= TStringList.Create;
List.AddObject(Humans[0].Name, TObject(Humans[0]));
List.AddObject(Humans[1].Name, TObject(Humans[1]));
List.AddObject(Humans[2].Name, TObject(Humans[2]));
List.Sort;
Human:= THuman(List.Objects[0]);
Showmessage('The first person on the list is the human ' + Human.name + '!');
List.Free;
End;