Java - Filter a list based on multiple values

Question

I am trying to filter out a list based on values. I have two List. One is a list of names which i want to remove i.e present in animalList. And another is the main primary list AnimalPrimaryDataPojoFilterList from where i have to remove the object which matches the names from animalList. Now i do have the solution but i think it takes lot of time. Below is the code. I am using Java 8. Can it be optimised?

if(animalList!=null && animalList.size()>0)
        {
            for(AnimalFilterPojo dtoObject:animalList)
            {
                if(!dtoObject.getApproved())
                {
                    for(AnimalPrimaryDataPojo mainDtoObject: AnimalPrimaryDataPojoFilterList)
                    {
                        if(mainDtoObject.getAnimalName().equalsIgnoreCase(dtoObject.getValue()))
                        {   
                            AnimalPrimaryDataPojoFilterList.remove(mainDtoObject);
                        }
                    }
                }
            }

If you want to remove elements from a list while iterating on it, you will have to manually instantiate the iterator and use iterator.remove() or you will have this problem. A better solution is to use stream(), filter() and collect(Collectors.toList()). — Arnaud Denoyelle
– Arnaud Denoyelle, Commented Nov 10, 2017 at 11:12
Optimized for what? Speed? Amount of braces? This piece of code is probably an indication of a larger design problem, so even if you convert this to use streams it won't really help. Your naming is also quite clumsy, adding Pojo to the end of a class name, especially when you then use dtoObject as a variable name. — Kayaman
– Kayaman, Commented Nov 10, 2017 at 11:55

Shubhendu Pramanik · Accepted Answer · 2017-11-10 11:09:48Z

2

Use removeAll() method.

AnimalPrimaryDataPojoFilterList.removeAll(animalList);

It will remove the objects of animalList from AnimalPrimaryDataPojoFilterList

N.B: You need to implement hashCode() and equals() method in AnimalFilterPojo

edited Nov 10, 2017 at 11:09

answered Nov 10, 2017 at 11:08

Shubhendu Pramanik

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2 Comments

sTg Over a year ago

Cannot use. Both list are different. AnimalPrimaryDataPojoFilterList has one of the property of animalList

Shubhendu Pramanik Over a year ago

@sTg Then how are you writing AnimalPrimaryDataPojoFilterList.remove(dtoObject); ?? it should be AnimalPrimaryDataPojoFilterList.remove(mainDtoObject);

Not a bug · Accepted Answer · 2017-11-10 11:42:56Z

1

You can use Java 8 streams to filter the list. In below example Parent is the object which has abc property of type String. We are filtering List<Parent> objs using List<String> names

public class ListFilterDemo {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        List<Parent> objs = new ArrayList<>();

        List<Parent> filtersObjs = objs.parallelStream().filter((obj) -> names.contains(obj.getAbc())).collect(Collectors.toList());
    }
}

class Parent {
    private String abc;

    public Parent(String abc) {
        this.abc = abc;
    }

    public String getAbc() {
        return this.abc;
    }
}

answered Nov 10, 2017 at 11:42

Not a bug

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Comments

user1708042 · Accepted Answer · 2017-11-10 13:21:34Z

You can try this:

if(animalList!=null && animalList.size()>0)
    animalList.removeIf(animal ->
        AnimalPrimaryDataPojoFilterList.stream()
           .filter(filter -> !filter.getApproved())
           .map(AnimalFilter::getValue)
           .collect(Collectors.toList()).contains(animal.getAnimalName()));

to explain the code: here we use removeIf() on the List to remove the objects using a Predicate that is a lambda that receives the animal and filters the list by removing the elements by name where name is taken from a list generated as a selection of the AnimalPrimaryDataPojoFilterList of the elments that have the approved flag (the second filter), extracting the value (using the map) and constructing a list out of it using a Collector.

The portion:

AnimalPrimaryDataPojoFilterList.stream()
   .filter(filter -> !filter.getApproved())
   .map(AnimalFilter::getValue)
   .collect(Collectors.toList())

generates the list to be used as a filter

animalList.removeIf(animal ->
    <generated list>.contains(animal.getAnimalName()));

uses list generated in place to apply the filter. Beware that this of course modifies the list you have Besides, you should not start a variable with a capital letter like you did for AnimalPrimaryDataPojoFilterList.

Ousmane D. · Accepted Answer · 2017-11-10 12:38:25Z

0

you can use removeIf then use AnimalPrimaryDataPojoFilterList as the source in which case you'll need to invert your logic within the if block i.e:

if(animalList != null && animalList.size() > 0){
      AnimalPrimaryDataPojoFilterList.removeIf(x -> 
                    animalList.parallelStream()
                   .filter(e -> !e.getApproved() && x.getAnimalName().equalsIgnoreCase(e.getValue())).findAny().orElse(null) != null);
}

edited Nov 10, 2017 at 12:38

answered Nov 10, 2017 at 11:14

Ousmane D.

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