data class precioSuper(var producto:String, var precio: Int, val codigoDeBarras:String)
fun main(args: Array<String>) {
//Qué vende o super?
val galletas = precioSuper("galletas", 3, "0001")
val chocolate = precioSuper("chocolate", 5, "0002")
val leite = precioSuper("leite", 2, "0003")
var productos = arrayListOf<String>("galletas", "chocolate", "leite")
var totalProductos = productos.size
var codigoDeBarras2 = for(producto in totalProductos)
}
in the lane of code var codigoDeBarras2 = for(producto in totalProductos) kotlin send me this error: "For-loop range must have an 'iterator()' method"
The error is exactly in "totalProductos" "for(producto in totalProductos)"
The error is that you are assigning the for loop to a variable.
for is not an expression and can't be assigned.
Also the expression producto in totalProductos does not make sense as you treat totalProductos like a Collection but it is only an integer number.
If you want to iterate through the items of the list productos you can do it:
for (producto in productos) {
//..............
}
or
for (i in 0 until totalProductos) {
//..............
}
or
productos.forEach {
}
Assume you are trying to "extract" the producto property of productos list. Then you can try
var codigoDeBarras2 = productos.map { it.producto }
Related
I got 2 lists with x objects inside , for example:
data class Model(
var token: String = "",
var id: String = "",
var name: String = "",
var image: Int = 0,
)
array is initialized and filled, the other list has x objects also that contains the objects of the first list but with different values in their properties!
what I want to do is to change the properties of the first array by the second one if they got the same object.name
var arr1 = ArrayList<Model>() // locale
var arr2 = ArrayList<Model>() // from db
the first array I got for example
[Model(name = "David", token = "" , image = 0)]
the second array I got
[Model(name = "David", token = "1asd5asdd851", image = 1)]
How do I make the first array take the missing token?
I tried with .filter{} and with .map{}. groupBy {} for hours because Name is the only properties that are the same but I'm more and more confused.
We can first group the second array by name using associateBy() and then iterate over first array and reassign properties:
val arr2ByName = arr2.associateBy { it.name }
arr1.forEach { item1 ->
arr2ByName[item1.name]?.let { item2 ->
item1.token = item2.token
item1.image = item2.image
}
}
Alternatively, if you don't need to modify items in arr1, but create another array and you can use items from both arr1 and arr2, then it will be much easier:
val arr3 = arr1.map { arr2ByName[it.name] ?: it }
One possible way would be to use fold() as follows:
fun main(args: Array<String>) {
val arr1 = listOf(Model(name = "David", token = "" , image = 0))
val arr2 = listOf(Model(name = "David", token = "1asd5asdd851", image = 1))
val mergedModels = arr2.fold(arr1) { localModels, dbModel ->
localModels.map { localModel ->
if (localModel.name == dbModel.name) localModel.copy(token = dbModel.token, image = dbModel.image)
else localModel
}
}
println(mergedModels)
}
If you want to reuse arr1 variable then you can do the following (but I would still use the previous option):
fun main(args: Array<String>) {
var arr1 = listOf(Model(name = "David", token = "" , image = 0))
val arr2 = listOf(Model(name = "David", token = "1asd5asdd851", image = 1))
arr1 = arr2.fold(arr1) { localModels, dbModel ->
localModels.map { localModel ->
if (localModel.name == dbModel.name) localModel.copy(token = dbModel.token, image = dbModel.image)
else localModel
}
}
println(arr1)
}
I have no idea what the error is, I am having a hard time adapting to this language, any help thank you very much.
Error:
Exception in thread "main" java.util.NoSuchElementException
at java.base/java.util.Scanner.throwFor(Scanner.java:937)
at java.base/java.util.Scanner.next(Scanner.java:1594)
at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
at Packing.<init>(Packing.kt:100)
at PackingKt.main(Packing.kt:7)
at PackingKt.main(Packing.kt)
My code:
import java.io.InputStream
import java.util.Scanner
fun main() {
val input = Scanner(InputStream.nullInputStream())
val packing1 = Packing(input)
val packing2 = Packing(input)
val packing3 = Packing(input)
var total = 0
var min = 0
val combinations = ArrayList<String>()
for(a in 1..3){
for(b in 1..3){
for(c in 1..3){
//here is a piece of code
}
}
combinations.sort()
println("${combinations.get(0)} $min")
}
}
class Packing {
var brownBottles = 0
var greenBottles = 0
var clearBottles = 0
constructor (input : Scanner){
brownBottles = input.nextInt() //this is the line 100
greenBottles = input.nextInt()
clearBottles = input.nextInt()
}
}
The idea is to enter values by console that initialize the variables of my objects.
I would just use
val input = Scanner(System.`in`)
If you enter 9 integers in the console the initialization of the Packing objects should work.
The nullInputStream() makes no sense to me. It's not possible to read from the console with that.
The combinations list is empty so it throws an exception accessing it here
println("${combinations.get(0)} $min")
I am trying to find the length of two different character array but I am only being allowed to use array.size only once.
How to bypass this problem?
fun chararraytostr(inp1: CharArray): String{
var arlen: Int = inp1.size //here lies the problem
var out1: String = ""
for(j in 0..arlen-1){
var str = inp1[j].toString()
out1+=str
}
return out1
}
fun uppercase(input: String): String{
var temp1: CharArray = input.toCharArray()
var len = input.size //here lies the problem
var temp3: Char
for(i in 0..len-1){
var temp2: Char = temp1[i]
var ascii: Int = temp2.toInt()
if(ascii<=122 && ascii>=97){
ascii-=32
temp3 = ascii.toChar()
temp1[i] = temp3
}else{}
}
var output = chararraytostr(temp1)
return output
}
fun main(arg: Array<String>){
var toupper = "Hi my friend!"
println(uppercase(toupper))
}
It is always showing Unresolved reference: size. I don't know why. Please help.
You're calling size on the String variable instead of the CharArray variable. Use temp1.size instead of input.size.
I have use two different classes:
ListTitle.kt
class ListTitle {
var id: Int? = null
var title: String? = null
constructor(id:Int, title: String) {
this.id = id
this.title = title
}
}
ListDes.kt
class ListDes {
var address: Int? = null
var des: String? = null
constructor(address: Int, des: String) {
this.address = address
this.des = des
}
}
listOfTitle and listDes are ArrayLists:
listOfTitle.add(ListTitle(1, "Hello"))
listOfTitle.add(ListTitle(2, "World"))
listDes.add(ListDes(1, "World Des"))
listDes.add(ListDes(2, "Hello Des"))
I want to assign title of ListTitle to des of ListDes by matching them by id/address for each element of the two lists.
How can I approach this?
You can use zip to merge two lists into one which has Pairs as elements.
val listOfTitle = listOf(ListTitle(1, "Hello"), ListTitle(2, "World"))
val listDes = listOf(ListDes(1, "World Des"), ListDes(2, "Hello Des"))
val pairList = listOfTitle.zip(listDes)
// since an element in the new list is a pair, we can use destructuring declaration
pairList.forEach { (title, des) ->
println("${title.title} ${des.des}")
}
Output:
Hello World Des
World Hello Des
A few notes:
You can write your classes in a shorter form in Kotlin. Just put the properties directly in the argument list of the primary constructor like shown below.
class ListTitle(
var id: Int? = null,
var title: String? = null
)
class ListDes(
var address: Int? = null,
var des: String? = null
)
Don't overuse nullability (using Int? instead of Int for instance). Make properties only nullable if necessary. If you always pass in arguments for the specified properties there is not need for them to be nullable.
Maybe you should choose other names for the classes (without "List" in it) since they are actually elements of a List in your example and not lists themselves.
If you just want to print the values you could do this:
listOfTitle.forEach {
val id = it.id
println(it.title + " " + listDes.filter { it.address == id }[0].des)
}
will print the matching des for each id:
Hello World Des
World Hello Des
The above code is supposed to work when both lists have the same length and there is always a matching des for each id
if you want to create a new list with the matching pairs:
val newList = listOfTitle.map { it ->
val id = it.id
Pair(it.title, listDes.filter { it.address == id }[0].des)
}
newList.forEach { println(it.first + " " + it.second) }
Previously I was using this code:
private val mItems = ArrayList<Int>()
(1..item_count).mapTo(mItems) { it }
/*
mItems will be: "1, 2, 3, 4, 5, ..., item_count"
*/
Now, I am using a class instead of Int, but the class has Int member with name id.
class ModelClass(var id: Int = 0, var status: String = "smth")
So how can I use this method to fill the ArrayList in similar way?
//?
private val mItems = ArrayList<ModelClass>()
(1..item_count).mapTo(mItems) { mItems[position].id = it } // Something like this
//?
From the mapTo documentation:
Applies the given transform function to each element of the original collection and appends the results to the given destination.
Therefore, you just need to return the elements you want:
(1..item_count).mapTo(mItems) { ModelClass(it) }
If you are OK with any MutableList (which is often ArrayList or similar):
val mItems1 = MutableList(item_count) { i -> i }
val mItems2 = MutableList(item_count) { ModelClass(it) }