How to arrange array of objects with same property value? - algorithm

Question

I have an person model with two property like this:
int id;
String name;
and some object with this data:
person0 = {1,"James"};
person1 = {2,"James"};
person2 = {3,"James"};
person3 = {4,"Barbara"};
person4 = {5,"Barbara"};
person5 = {6,"Ramses"};
and array contain objects:
firstArray = [person0, person1, person2, person3, person4, person5];
Therefore how can have this array:
secondArray = [
[person0, person1, person2],
[person3, person4],
[person5]
]
Thank you.

Answer 1

If language does not matter.
map = new Map();
for (persona of personas) {
name = persona.name;
arrayForName = map.get(name);
if (arrayForName == null) {
arrayForName = [];
map.put(name, arrayForName);
}
arrayForName.put(persona)
}
The idea is to have a map (which is a collection key->value).
The value of the map should in turn be an array.
To add elements efficiently, you iterate only once through the data, and add arrays each time a new key is discovered (i.e. the name).
In Java it would be something like:
Map<String, List<Persona>> map = new HashMap<>();
for (Persona persona : personas) {
String name = persona.getName();
List<Persona> listForName = map.get(name);
if (listForName == null) {
listForName = new ArrayList<Persona>();
map.put(name, listForName);
}
listForName.add(persona)
}

Answer 2

Try this code in Java Android:
ArrayList<ArrayList<Person>> secondArr = new ArrayList<>();
ArrayList<Course> tempArr = new ArrayList<>();
for (int i = 0; i < firstArr.size(); i++) {
if ((i + 1) >= firstArr.size()) {
tempArr.add(firstArr.get(i));
secondArr.add(tempArr);
} else {
if (firstArr.get(i).name .equals( firstArr.get(i + 1).name) ) {
tempArr.add(firstArr.get(i));
} else {
tempArr.add(firstArr.get(i));
secondArr.add(tempArr);
tempArr = new ArrayList<>();
}
}
}
Finally secondArr prepared.
And if list not sorted we can use code like this:
for (int i = 0; i <firstArr.size() ; i++) {
boolean isAdd = false;
for (int j = 0; j < secondArr.size() ; j++) {
if (secondArr.get(j).get(0).getName().equals(firstArr.get(i).getName())){
secondArr.get(j).add(firstArr.get(i));
isAdd =true;
break;
}
}
if (!isAdd){
ArrayList<Person> arrayList = new ArrayList<>();
arrayList.add(firstArr.get(i));
secondArr.add(arrayList);
}
}