Try this.

List<String> list = List.of(
    "1", "1.1", "1.2", "1.3",
    "2", "2.1", "2.2", "2.3",
    "3", "3.1", "3.2", "3.3", "3.4", "3.5", "3.6", "3.7", "3.8", "3.9", "3.10",
    "4", "4.1", "4.1.1", "4.1.1.1", "4.1.1.2", "4.1.2", "4.1.2.1", "4.1.2.2", "4.2", "4.2.1", "4.2.2", "4.3",
    "5", "5.1");
Set<String> fathers = list.stream()
    .map(e -> e.replaceAll("\.\d+$", ""))
    .collect(Collectors.toCollection(LinkedHashSet::new));
System.out.println(fathers);

output

[1, 2, 3, 4, 4.1, 4.1.1, 4.1.2, 4.2, 5]

I have an arraylist with these values (the values can change):

1  
1.1
1.2
1.3
2  
2.1
2.2
2.3
3  
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
4  
4.1
4.1.1
4.1.1.1
4.1.1.2
4.1.2
4.1.2.1
4.1.2.2
4.2
4.2.1
4.2.2
4.3
5  
5.1

I need to identifiy the fathers value in an arraylist, for this case, the arraylist has this fathers values:

1, 2, 3, 4, 4.1, 4.1.1, 4.1.2, 4.2, 5

enter image description here

for example, in this picture the “fathers values” (1, 1.3) can’t be selected, because it has child options.

I have an spinner in an android app, and I want to do something like that, the idea is in the spinner only parent values are hidden or cannot be selected. I don’t have idea how can I do with this exercise.

Any idea? Please