kotlin

How can I get a specific property of an object using filter in Kotlin?

In Kotlin I have the following objects:

data class BugReport(
    val message: String,
    val bugItems: List<BugItem>,
)

And:

data class BugItem(
    val title: String,
    val checked: Boolean = false,
)

In a BugReport object, how can I get only the title property of those BugItems whose checked value is equal to true.

The idea is to get a comma separated string from the title.

I have this code:

val checkedTitles = bugReport.bugItems.filter(BugItem::checked).joinToString()

But with this code I get the complete BugItem objects, how can I get only the title property?

Solution

  • The last parameter of joinToString allows you to pass a function that transforms the objects to CharSequences, so you can do

    val checkedTitles = bugReport.bugItems
    .filter(BugItem::checked)
    .joinToString { it.title }

    If you want a List<String> containing the titles instead, you should use map to transform the objects.

    // checkedTitles is of type List<String>
val checkedTitles = bugReport.bugItems
    .filter(BugItem::checked)
    .map(BugItem::title)