Originally posted by: DanielFelixFerber

I would appreciate your advice about pros/cons of storing attributes on tuple sets or on arrays.

The model that reads an enumeration of "objects" that are identified by two key integers "i" and "j".
The object has some attributes. "attr1" and "attr2".

(1) I have declared the enumeration of the objects as:

tuple tplObject {
key int i;
key int k;
int attr1;
string attr2;
}
{tplObject} objects = ...;

(2) An alternative model could declare the same as:

tuple tplObject {
key int i;
key int k;
}
{tplObject} objects = ...;
tuple tplObjectData {
int attr1;
string attr2;
}
{tplObjectData } objectDatatplObject = ...;

I wonder about the pros/cons of (1) and (2). Are there memory/performance benefits? O other advices or best practices about choosing among (1) and (2)?

I think that (1) leads to a data file that might be easier to read as all data of an individual object stays together.
But (2) produces a model that is easier to read, since I can get an attribute as simply as "objectDataobj.attr1".

Best regards,
Daniel Felix Ferber
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Originally posted by: SystemAdmin

Daniel,

what you will typically have is a mixture of both.
Ti initialize extrenal data you will use (1), as this
e.g. the only way to read data from a database. And as
you told, data elements are kept together.

To optimize code performance you will copy the elements
of the tuple-set to an array as you described.
Memory is doubled at that moment but array access
is much faster than the "find" in the tuple set.
So far, in my applications memory requirements were
a minor topic than performance.
(Please note that it should be declared as

{tplObjectData } objectData[objects] = ...;

)

I hope these remarks are ofany help to you.

Regards
Norbert

Hope this will help
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Originally posted by: DanielFelixFerber

Thanks for the clarification.

BTW, it was not trivial for me to discover the expression that gets attributes from a tuple that has to be "found" withing a set. Therefore I would like to share it with the community:

item(objects, <i, k>).attr1
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Originally posted by: SystemAdmin

Just for sake of completeness

var tpl = objects.find(i,k);
 if(tpl!= null)
 {
    writeln(" Found : ", tpl.attr1);
 }
 else
   writeln("Not found ....");

should work as well.

To the best of my knowledge, your solution might result in a
null-pointer-access when the element is not found ...

Regards
Norbert
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Originally posted by: SystemAdmin

You are right, item and ord for example will raise an error if the tuple can not be found.
By the way, the script can sometimes be slow.

A workaround can be to protect the statement with the ?: syntax.
Example:

tuple T{
int a;
int b;
};
 
{T} S = {<i,j> | i in 1..10,j in 1..5}; //j not in 1..10
 
// we will iterate on j in 1..10 to get through the holes.
int X = sum(i,j in 1..10) ( <i,j> in S ? item(S, <i,j>).a : 0);
execute{
writeln(X);
}

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Hi

I am not sure that you would get a null pointer in this case, I think you would simply get en error.

For example

tuple t
{
 int a;
 int b; 
}  
 
{t} s={<1,2>};
 
execute
{
 s; 
}  
 
int r1=item(s,<1,3>).b;
execute
{
 writeln(r1); 
}

gives

OPL cannot extract expression: item(s,<1,3>).

Alex
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Originally posted by: joaoamorim

Hi

I am still getting started in OPL, and I am having a similar problem.

In the DB I have a table with this info:

tuple costData {
string Car;
string Parking;
int Period;
int Cost;
}

{costData} CostData = ...;

Assuming I have already got the Cars, Parkings and Periods, how do I transfer the info from CostData set to this array:

int CostsCarsParkingsPeriods

Also, do you know where to find some good tutorials / info about OPL?

Thanks
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Originally posted by: SystemAdmin

Using generic index initialization, you could declare and initialize the array as follows:

int CostsCarsParkingsPeriods[Cars][Parkings][Periods] = [cd.Car: [cd.Parking : [cd.Period: cd.Cost]] | cd in CostData ];

Just be aware that if you don't have Cost data for each combination of Car+Parking+Period, a default value of 0 will be set.
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