HI all - I would really appreciate some guidance on extracting values and/or indexes from a List. I'...

# getting-started

[CanOfBees]

HI all - I would really appreciate some guidance on extracting values and/or indexes from a List. I'm working on some of the hyperskill courses and one question is returning the index of a given value - which may be duplicated- from a list.

Given the following list:

val products = listOf("milk", "eggs", "bread", "cheese", "eggs", "greens")

return the index(es) of a given string; e.g. "eggs" should return 1 4. After some experimenting I've been trying to use forEachIndexed(), but I don't know how to express 'print $index where $value == "eggs"'. Can someone provide any pointers? Alternate approaches are welcome, of course 😄

Thanks in advance for your help!

val products = listOf("milk", "eggs", "bread", "cheese", "eggs", "greens")
products.forEachIndexed { index, s -> println("${s} ${index}") }
products.forEachIndexed { index, s -> ??? }

[Higor Oliveira]

I think you can use this approach.

val products = listOf("milk", "eggs", "bread", "cheese", "eggs", "greens")
products.forEachIndexed {  index, s ->  
    // eggs inside if should be replaced to a variable that has the value you want to find
    if (s == "eggs" ) {
        println("${s} ${index}")
    }
}

[CanOfBees]

@Higor Oliveira thanks for your reply! I was chewing away at it and hit something similar, now trying to resolve type mismatches 😄 . I appreciate the help 🙂

[Vampire]

println(
    products
        .zip(0..<products.size)
        .filter { it.first == "eggs" }
        .joinToString(" ") { "${it.second}" }
)

[CanOfBees]

Hi Björn - that is great! Thank you

[Riccardo Lippolis]

FYI, there's also a convenient withIndex() function, so that you don't need to zip with the index manually, it would look something like this:

println(
    products
        .withIndex()
        .filter { it.value == "eggs" }
        .joinToString(" ") { "${it.index}" }
)

[CanOfBees]

@Riccardo Lippolis thank you for that example - very, very neat!

[Huib Donkers]

See also the solution here: https://kotlinlang.slack.com/archives/C0B8MA7FA/p1720022708041039?thread_ts=1720022708.041039&cid=C0B8MA7FA