基于番石榴的一种特性对列表进行过滤 [英] Filtering on List based on one property with guava
问题描述
我有一个叫做Person的课程-
I have a class called Person -
public class Person implements Nameable {
private String name;
public String getName(){
return name;
}
}
现在我有两个列表-
List<Person> persons = // some persons
List<Person> subsetOfPersons = // some duplicate persons, but different objects and don't share the same identity
现在我想过滤subsetOfPersons
中不存在的persons
,相等标准是name属性,Person没有相等.
Now I would like to filter the persons
which are not present in the subsetOfPersons
, equality criteria is name property and Person doesn't have equals.
我该怎么做?
推荐答案
我敢肯定有一种更简单的方法...为了进行比较,下面将把人转换为姓名.对于subsetOfPersons
,我们实际上直接创建了一个名称列表,因为这是我们真正需要它们的全部.对于persons
,我们将转换限制在比较的上下文中.
I'm sure there's a simpler way... the below would transform person to name for the sake of comparison. For the subsetOfPersons
, we actually create a list of names directly, since that's all we really need from them. For the persons
, we keep the transformation limited to the context of the comparison.
Iterable<Person> filtered = Iterables
.filter(
persons,
Predicates.not(
Predicates.compose(
Predicates.in(ImmutableSet.copyOf(Iterables.transform(subsetOfPersons, personToNamefunction))),
personToNamefunction
)
)
);
编辑:以为您可能会喜欢JUnit:
Edit: Thought you might appreciate a JUnit:
package com.stackoverflow.test;
import static org.junit.Assert.*;
import java.util.Iterator;
import org.junit.Test;
import com.google.common.base.Function;
import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
public class PersonTest {
public class Person {
private String name;
public String getName(){
return name;
}
public void setName(String name) {
this.name = name;
}
}
@Test
public void testNameBasedFiltering() {
Person bob = createPerson("bob");
Person jim = createPerson("jim");
Person pam = createPerson("pam");
Person roy = createPerson("roy");
ImmutableList<Person> persons = ImmutableList.of(
bob,
jim,
pam,
roy);
ImmutableList<Person> subsetOfPersons = ImmutableList.of(
createPerson("jim"),
createPerson("pam"));
Function<Person, String> personToNamefunction = new Function<Person, String>() {
public String apply(Person arg0) {
return arg0.getName();
}
};
Iterable<Person> filtered = Iterables
.filter(
persons,
Predicates.not(
Predicates.compose(
Predicates.in(ImmutableSet.copyOf(Iterables.transform(subsetOfPersons, personToNamefunction))),
personToNamefunction
)
)
);
for (Person person : filtered) {
assertNotSame(jim, person);
assertNotSame(pam, person);
}
}
public Person createPerson(String name) {
Person person = new Person();
person.setName(name);
return person;
}
}
再次编辑:首次缺少"not"要求.易于修复-有了谓词,您就可以用Predicates.not(..)
包装!
Edit again: Missed the "not" requirement the first time. Easy fix--with predicates, you can just wrap with Predicates.not(..)
!
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