[Interest] Best practice for sorting multiple (connected) QLists

[andre at familiesomers.nl]

Joshua Grauman schreef op 19.11.2013 21:26:
> I fairly often find myself wanting to sort a bit of data. Imagine I 
> have a
> few QList<int>'s a QStringList's and that they correspond like a 
> database
> table so that I always append to all the lists together with data for 
> one
> row. Something like:
> 
> QList<int> age, height;
> QStringList firstname, lastname;
> while(data)
> {
>     age.append(getData1());
>     height.append(getData2());
>     firstname.append(getData3());
>     lastname.append(getData4());
> }
> 
> Now what if I want to sort all that data, (say by age) so that I can 
> print
> out all the first and last names in order according to age.

I think your problem is in your data structure. Instead of using 
separate containers for each of the fields, you should use a single 
container with all of the fields:

struct Person
{
     int age;
     int height;
     QString firstName;
     QString lastName;
}

QList<Person> persons;
while(data)
{
     Person person;
     person.age = getData1();
     person.height = getData2();
     person.firstName = getData3();
     person.lastName = getData4();
     persons.append(person);
}

Now, you can easily sort the persons list itself by using qSort with a 
comparison function for the field you want to sort on, or keep track of 
the order by using a QMap<key, int> using the index into the persons 
list as the value of your map.

Alternatively, look into Boost.MultiIndex.

André

> 
> I've tried different ways of doing this, but they all seem a bit
> contrived. The best I've come up with is to have another QMap<int, int>
> that maps the sorting order to the indices like:
> 
> QList<int> age, height;
> QStringList firstname, lastname;
> QMap<int, int> order;
> while(data)
> {
>     age.append(getData1());
>     height.append(getData2());
>     firstname.append(getData3());
>     lastname.append(getData4());
>     order[age.last()] = age.size()-1;
> }
> 
> QList<int> orderedIndices = order.values();
> 
> for(int i=0; i<orderedIndices.size(); i++)
> {
>    print(firstname[orderedIndices[i]], lastname[orderedIndices[i]]);
> }
> 
> It's not too bad. I'm not worried about performance, most of the time
> these are just small amounts of data that don't warrant creating a new
> class to handle, or creating a database for. I'm just wondering if 
> anyone
> has a cleaner way of handling this? What do you do for these types of
> situations?
> 
> Josh
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