Use of ArrayList

[stainless]

I am not very experienced with C# and have a question regarding
storing and accessing data in an array list.

Whilst reading a datarow sorted on 3 fields (thID, dthID and locID -
all 3 are type int), I need to store unique combinations of the 3
values in an arraylist, and then be able to access the combinations
later. I am fine with the reading of the datarow and identifying the
unique combinations, but am struggling with how I would then store
these in the array list.

For example:

thID dthID locID
----- ------ -------

1 1 1
2 1 1
2 1 2
2 2 2
2 4 2
3 4 3


How would I define the arraylist, add the data each time and then
access these values later?

Cheers

Mark

 

[Farrukh]

As far I understand from your question, you may need to use Two
Dimensional Array or may be Multidimensional array according to the
requirements:
Here is a Raw example which might be helpful to you:

using System;

class TwoD {
public static void Main() {
int t, i;
int[,] table = new int[6, 3]; //Declaring the array
/* This is the array named "table" of 6 Rows and 3 Columns/Fields i.e.
for each row there are 3 columns/fields. You can increase the number
of rows according to your data size.

for each row there would be a combination of 3 columns.
*/

// Data for Row 1
table[0,0]=1;
table[0,1]=1;
table[0,2]=1

// Data for Row 2
table[1,0]=2;
table[1,1]=1;
table[1,2]=1

// Data for Row 3
table[2,0]=2;
table[2,1]=1;
table[2,2]=2

// go on up to 5
table[5,0]=5;
table[5,1]=1;
table[5,2]=3

}
}
}



Here is an illustration for this:

Columns
thID | dthID | locID
Rows-------------------------------------------
R1 1 | 1 | 1
R2 2 | 1 | 1
R3 2 | 1 | 2
R4 2 | 2 | 2
R5 2 | 4 | 2
R6 3 | 4 | 3



You can use some Loop statement like "for" to access the combinations
Hope this helps.

 

[stainless]

Thanks

This may work but I understood that an array has to be defined as a
fixed size up front (in your answer, you define the array at start of
processing as int[,] table = new int[6, 3]). Thus, if I knew there
would be a maximum of 6 occurrences, this would work.

However, I do not know how many occurrences there are of the 3 values
(my example was 6 but until I have built the list, I will not know
what the size needs to be), thus I need to be able to add to the end
of the list. This is why I thought an arraylist would be the better
option as, if I understand correctly, this does not have to be defined
as a fixed size up front.

Cheers

Mark

 

[Farrukh]

Mark,

I'm sorry, that example was just to give an idea, even to myself

I suggest, you should use structure and define your ArrayList in that
structure..

Thanks

This may work but I understood that an array has to be defined as a
fixed size up front (in your answer, you define the array at start of
processing as int[,] table = new int[6, 3]). Thus, if I knew there
would be a maximum of 6 occurrences, this would work.

However, I do not know how many occurrences there are of the 3 values
(my example was 6 but until I have built the list, I will not know
what the size needs to be), thus I need to be able to add to the end
of the list. This is why I thought an arraylist would be the better
option as, if I understand correctly, this does not have to be defined
as a fixed size up front.

Cheers

Mark

As far I understand from your question, you may need to use Two
Dimensional Array or may be Multidimensional array according to the
requirements:

 

[Guest]

Stainless,
An ArrayList holds type Object, there is nothing to define.
If you don't know how many elements each of your "objects" will have, you
can even store individual ArrayList instances in each main ArrayList element.

Peter

 

[Rick Lones]

I am not very experienced with C# and have a question regarding
storing and accessing data in an array list.

Whilst reading a datarow sorted on 3 fields (thID, dthID and locID -
all 3 are type int), I need to store unique combinations of the 3
values in an arraylist, and then be able to access the combinations
later. I am fine with the reading of the datarow and identifying the
unique combinations, but am struggling with how I would then store
these in the array list.

For example:

thID dthID locID
----- ------ -------

1 1 1
2 1 1
2 1 2
2 2 2
2 4 2
3 4 3


How would I define the arraylist, add the data each time and then
access these values later?

Not entirely clear what you are trying to do - is it something like:

class RowKey
{
int thID;
int dthID;
int locID;

void RowKey(th, dth, loc)
{
thID = th;
dthID = dth;
locID = loc;
}
}

ArrayList list = new ArrayList();
list.Add(new RowKey(1,1,1));
list.Add(new RowKey(2,1,1));, etc. ??

You could then use constructs like:
foreach (RowKey rk in list) { . . . } or RowKey rk = (RowKey)list, etc.

If this is what you are after (more or less), then you could look into
List<RowKey> (the generic). Also, if you want to preserve the order by sorting
your list you may want to implement IComparable on the RowKey class . . .

HTH,
-rick-

 

[stainless]

Thanks everyone

I think I have the solution now based on Farrukh's suggestion of using
structs. I have defined a struct as below:

public struct UniqueLocation
{
public int alocID;
public int dthID;
public int thID;

}


Then, I can add populated instances of this struct to my arraylist
e.g.

arrayListname.Add(currentLocation);

I have to admit I haven't fully tested this yet (due to other C#
issues I am working through) but the concept looks fine.

Cheers

Mark

 

[Peter Duniho]

[...]
Then, I can add populated instances of this struct to my arraylist
e.g.

arrayListname.Add(currentLocation);

I have to admit I haven't fully tested this yet (due to other C#
issues I am working through) but the concept looks fine.

It probably is fine. However, you should definitely consider Rick's
suggestion to use the List<> generic class, especially since you are
storing the data in structs instead of classes. You can declare an
appropriate instance like this:

List<UniqueLocation> arrayListname = new List<UniqueLocation>();

IMHO, the primary advantage is that, if I recall correctly, using the
List<> generic class there is no boxing/unboxing overhead when using a
struct type (this wouldn't be an issue if you were using a class instead
of a struct), as there would be when using the ArrayList class. Another
advantage is the compile-type type-checking you get from using the generic
class.

Pete

 

[Jon Skeet [C# MVP]]

Thanks everyone

I think I have the solution now based on Farrukh's suggestion of using
structs. I have defined a struct as below:

public struct UniqueLocation
{
public int alocID;
public int dthID;
public int thID;

}

Not good on three fronts:

1) Do you really want the locations being boxed and unboxed all over
the place? Why did you decide to use a struct instead of a class?

2) Using public fields is a recipe for disaster

3) Mutable value types are a bad idea - they're likely to cause
confusion, particularly when you combine them with boxing.

I'd echo the other posters: use a List<T>, and define a class with
appropriate members, properly encapsulated in properties.