made these as an exercise, then found out they were in sequence. oh well.

kotlinlistmethods.kt

package com.lacronicus.kotlinlistmethods

import java.util.ArrayList


/**
 * Created by fdoyle on 11/13/15.
 */

fun <T, R> List<T>.map(mapFunc: (T) -> R) : List<R> {
    val rs = ArrayList<R>(this.size())
    for (value in this) {
        rs.add(mapFunc.invoke(value))
    }
    return rs
}

fun <T> List<T>.filter(filterFunc: (T) -> Boolean) : List<T> {
    val ts = ArrayList<T>()
    for (value in this) {
        if (filterFunc.invoke(value))
            ts.add(value)
    }
    return ts
}


fun <T, R> List<T>.flatMap(mapFunc: (T) -> List<R>) : List<R> {
    val rs = ArrayList<R>()
    for (value in this) {
        val newValueList = mapFunc.invoke(value)
        for(newValue in newValueList)
            rs.add(newValue)
    }
    return rs
}

fun <T> List<T>.doOnEach(doOnEach: (T) -> Unit){
    for (value in this) {
        doOnEach.invoke(value);
    }
}

Like i said, probably best to use Sequence, but for something quick and dirty, this'll do the job.

For reference, you can do:

myList.iterator().toSequence().map/filter/whatever

or something like that.