D-Net

import eu.dnetlib.pace.common.AbstractPaceFunctions;

import eu.dnetlib.pace.model.Field;

import java.util.HashSet;

import java.util.List;

import java.util.stream.Collectors;

public class UrlClustering extends AbstractPaceFunctions implements ClusteringFunction {

    protected Map<String, Integer> params;

    public UrlClustering(final Map<String, Integer> params) {

        this.params = params;

    public Collection<String> apply(List<Field> fields) {

        return fields.stream()

                .filter(f -> !f.isEmpty())

                .map(Field::stringValue)

                .map(this::asUrl)

                .map(URL::getHost)

                .collect(Collectors.toCollection(HashSet::new));

    @Override

    public Map<String, Integer> getParams() {

        return null;

    }