Filter list of objects based on list of object properties

Question

What is the best way to filter out a list of objects with a list of properties of the given object.

Here is the sample code that shows what I'm trying to achieve:


    data class Person(
            val id: Long = 0,
            val name: String = ""
    )

    fun filterOutList(): List<Person>{

        val idsToRemove = listOf(1, 3)

        val listToFilter = listOf(
                Person(1, "John"),
                Person(2, "Jane"),
                Person(3, "Bob"),
                Person(4, "Nick")
        )

        // expecting to get a list only with Objects that have ids 2 and 4

        return listToFilter.filter { ??? provide `idsToRemove` to get only what was not in the list  }
    }

IlyaMuravjov · Accepted Answer · 2019-10-12 19:45:17Z

2

Do it this way: return listToFilter.filter { it.id !in idsToRemove }.

To get it compiled, you should explicitly specify the <Long> type parameter when you create idsToRemove: listOf<Long>(1, 3) or listOf(1L, 3L). The compiler infers the <Int> type parameter implicitly.

answered Oct 12, 2019 at 19:45

IlyaMuravjov

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Comments

Jakub Kostka · Accepted Answer · 2019-10-12 19:30:26Z

0

You can use native method filter{ }. As following:

return listOf(
                Person(1, "John"),
                Person(2, "Jane"),
                Person(3, "Bob"),
                Person(4, "Nick")
        ).filter{ it.id == 2 || it.id == 4 }

answered Oct 12, 2019 at 19:30

Jakub Kostka

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1 Comment

Maksim Over a year ago

This is kinda hard coding. What if idsToRemove is a dynamic array?

Maksim · Accepted Answer · 2019-10-12 20:04:14Z

0

I found following solution that worked for me:

val filteredResponse = listToFilter.filter { ! idsToRemove.contains(it.id) }

But as @Bananon mentioned, I had to explicitly specify idsToRemove: listOf<Long>(1, 3)

answered Oct 12, 2019 at 20:04

Maksim

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