I have a data class in Kotlin like this:
data class Activity(
var id: String? = "",
var prize: MutableMap<String?, Int?>? = null
)
And a list of this object:
var myList = listOf(Activity("A", prize={day_5=70, day_4=70}),
Activity("B", prize={day_5=40, day_4=80}))
The desired result is:
Activity("A", prize={total=140}),
Activity("B", prize={total=120})
So basically I want to sum the values of the prize map inside of each object.
I think that has something to do with transformation but I'm new to Kotlin and I couldn't find any resources over the internet, or maybe they were to complicated.
This algorithm is easy, just iterating through all the maps and replace elements with the sum:
val myList = listOf(
Activity("A", hashMapOf("day_5" to 70, "day_4" to 70)),
Activity("B", hashMapOf("day_5" to 40, "day_4" to 80)),
)
for (i in myList) {
val total = i.prize.values.sum()
i.prize.clear()
i.prize["total"] = total
}
Related
I'm trying to build a simple app that would display a coin collection for each user I type into a textfield. The coin collection would have to be unique to each user. I already have the repository for the coins. How do I generate a new random coin collection for each user? Each collection could have multiple coins of the same value but with different years.
object CoinRepository {
fun getCoinCollection(): List<Coin> {
return listOf(
Coin(
id = 1,
name = "Penny",
year = (1900..2022).random()
),
Coin(
id = 2,
name = "Nickel",
year = (1900..2022).random()
),
Coin(
id = 3,
name = "Dime",
year = (1900..2022).random()
),
Coin(
id = 4,
name = "Quarter",
year = (1900..2022).random()
),
Coin(
id = 5,
name = "Dollar",
year = (1900..2022).random()
)
)
}
}
data class Coin(
val id: Int,
val name: String,
val year: Int
)
You could do something like this:
import kotlin.random.Random
// Define your specific data in an enum, with all the relevant properties
enum class Denomination(val id: Int, val label: String) {
PENNY(1, "Penny"),
NICKEL(2, "Nickel"),
DIME(3, "Dime"),
QUARTER(4, "Quarter"),
DOLLAR(5, "Dollar");
companion object {
// a simple way to return one of the instances at random - the property
// avoids creating a new values() array every time it's called
val values = values()
fun random() = values.random()
}
}
// a basic way to keep the random date logic in the Coin class itself, using
// a default parameter. No validation involved obviously!
data class Coin(val id: Int, val label: String, val year: Int = (1900..2022).random())
// get a random number of Coins, within a certain min/max
fun getCoinCollection() = List(Random.nextInt(1, 10)) {
// pulls a random coin type and creates a Coin, letting its constructor
// handle the random date (you could do it here if you want)
Denomination.random().run { Coin(id, label) }
}
There's more than one way to organise it, I've thrown a few things in there so you can get some ideas of how you might do it. But it's basically a function that creates a list of random length (within limits), and then creates a Coin for each item, using a random Denomination
The Denomination enum is just a way to define your data, a fixed set of possible items with certain properties. Because enums generate that values() array automatically (containing all its instances) you can easily pick one at random. You could also extend the properties here to include a valid date range for each coin type, etc
You could just automatically generate the label and id values from the enum's name and ordinal properties (e.g. "PENNY" and 0) so you don't need to declare them explicitly - I feel like it's usually a good idea to decouple the data from how it's represented in the enum in code, but that's your call - I've included it so you can see how
for (i in 0 until result.size){ result[i].config= addConfig(taskNames!![i],processKeys!![i]) }
Here result is a list of class which has datamember config and tasNames and processKeys are list of string.
Is there a way in kotlin to map result.config with respective taskNames and processKeys without using traditional loop and mentioning length of result.I am new to kotlin.
class Process {
var processKey: String? = null
var task: List<Task>? = null}
class Task {
var taskName: String? = null
var processVariables: List<ProcessVariable>? = null}
class ProcessVariable {
var name: String? = null
var label: String? = null
var applicableValue: List<String>? = null}
Result is already present with datamember config pf type ProcessVariable
If I understand your problem correctly, you need to combine 3 lists.
So iterating over the lists may be easier to understand than some clever way of list transformations.
You can get rid of the traditional for loop, so you don't need to calculate the size of the loop:
result.forEachIndexed {
i, resultData -> resultData.config = addConfig(taskNames[i], processKeys[i])
}
If you want to combine two lists, you can use the zip method:
val configList = taskNames.zip(processKeys) {tsk, prc -> addConfig(tsk, prc)}
In your example, the result-object was already existing. Maybe it is easier to create new result-objects:
val results = configList.map {
Result(config = it)
}
I want to create zero padding ArrayList, like this.
val ls = arrayListOf<Int>(0,0,0,0,0)
Is there a way to create n-size zero padding array list than using loop?
// can create zero padding array list but not looks smart
val ls = arrayListOf<Int>()
for (i in 0..n){
ls.add(0)
}
You can create a MutableList (or a List) with size 5 filled with zeros:
val list = MutableList(5) { 0 }
and if you want it as an ArrayList:
val arrayList = ArrayList(list)
or:
val arrayList = ArrayList(MutableList(5) { 0 })
You can also do the following
var arrayList = IntArray(5).toCollection(ArrayList(5))
or following, because as of now MutableList returns an ArrayList
var mutableList = MutableList(5){0} as ArrayList<Int>
but this may break if MutableList changes to something other than ArrayList(may be LinkedList) in future and should be avoided.
In Kotlin, how can I take the first n elements of this array:
val allColours = arrayOf(
Pair(Color.RED, Color.WHITE),
Pair(Color.RED, Color.BLACK),
Pair(Color.YELLOW, Color.BLACK),
Pair(Color.GREEN, Color.WHITE),
Pair(Color.BLUE, Color.WHITE),
Pair(Color.BLUE, Color.WHITE),
Pair(Color.CYAN, Color.BLACK),
Pair(Color.WHITE, Color.BLACK))
So how can I fill pegColours with the first say 3 Pairs?
var pegColours: Array<Pair<Color,Color>> = //???
I tried allColours.take but it gave an error:
Expecting an element
You need to specify the number of items you want to take.
allColours.take(3)
For a random number of random indices, you can use the following:
val indexes = arrayOf(2, 4, 6)
allColours.filterIndexed { index, s -> indexes.contains(index) }
Note that you can write an extension method for this:
fun <T> Array<T>.filterByIndices(vararg indices: Int) = filterIndexed { index, _ -> indices.contains(index) }
Alternatively, if the indices are consecutive, you can use slice:
allColours.slice(1..3)
The problem with your code that you create pairs with color constants which are Ints (allColours has type Array<Pair<Int, Int>>), but you expect Array<Pair<Color, Color>>. What you have to do is change type pegColours type and use take:
var pegColours: Array<Pair<Int, Int>> = allColours.take(3).toTypedArray()
Also you have to call toTypedArray() cause Array.take returns List rather than Array. Or you can change pegColours type as following:
var pegColours: List<Pair<Int, Int>> = allColours.take(3)
I know you already proposed the usage of take, but alternatively ranges and a simple map also help to write idiomatic code as shown next:
var pegColours = (0 until 3)
.map { allColours[it] }
.toTypedArray()
You are very close :)
val allColours = arrayOf("red", "blue", "green")
kotlin.io.println(allColours.take(2))
Will give you first two elements ["red", "blue"]
You have to specify the number of elements you want to take from the array
I have a string array and an integer array. How do I create a map using the first as keys and the second as values?
val keys = arrayOf("butter", "milk", "apples")
val values = arrayOf(5, 10, 42)
val map: Map<String, Int> = ???
How to convert List to Map in Kotlin? doesn't solve this problem; I have 2 arrays and want a single map.
You can zip together the arrays to get a list of pairs (List<Pair<String, Int>>), and then use toMap to get your map.
Like this:
val keys = arrayOf("butter", "milk", "apples")
val values = arrayOf(5, 10, 42)
val map: Map<String, Int> =
keys.zip(values) // Gives you [("butter", 5), ("milk", 10), ("apples", 42)]
.toMap() // This is an extension function on Iterable<Pair<K, V>>
According to kotlin
Constructing Collections
-> creating a short-living Pair object, is not recommended only if performance isn't critical and to quote: "To avoid excessive memory usage, use alternative ways. For example, you can create a mutable map and populate it using the write operations. The apply() function can help to keep the initialization fluent here."
since I'm not much of an expert I run on to these code and maybe this should work better?:
val numbersMap = mutableMapOf<String,Int>()
.apply{ for (i in 1.. 5) this["key$i"] = i }
println(numbersMap)
//result = {key1=1, key2=2, key3=3, key4=4}
or to adjust it to question above - something like this:
val keys = arrayOf("butter", "milk", "apples")
val values = arrayOf(5, 10, 42)
val mapNumber = mutableMapOf<String, Int>()
.apply { for (i in keys.indices) this[keys[i]] = values[i] }
println(mapNumber)