I want to get a list of String in ArrayList<Array<String>> by using stream() and map in Kotlin.
Each Array<String> of my arrayList has 3 values and I want to get the first index value and the last index value of each array.
This is my code:
fun main(args: Array<String>) {
val result: List<String>
val obj1 = arrayOf("fruit", "Mangue", "Africa")
val obj2 = arrayOf("Milk", "Soja", "Europ")
val obj3 = arrayOf("Meat", "cochon","Asia")
val myArrayList: ArrayList<Array<String>> = ArrayList<Array<String>>(3)
val myList: MutableList<Array<String>> = mutableListOf<Array<String>>()
myList.add(obj1)
myList.add(obj2)
myList.add(obj3)
myArrayList.addAll(myList)
result = myArrayList.stream().map{it -> ("${it[0]}-${it[2]}")}.toList()
println("ArrayList of objects :")
println(myArrayList)
println("my list of String result")
println(result)
}
I want to have this list of String in my result:
[fruit-africa,milk-Europ,Meat-Asia]
Also, when I print myArrayList, I have a bad result:
ArrayList of objects :
[[Ljava.lang.String;#5caf905d, [Ljava.lang.String;#27716f4, [Ljava.lang.String;#8efb846]
How can I do it, please?
Your Question
When I run your code, this is the output I see:
ArrayList of objects :
[[Ljava.lang.String;#5b480cf9, [Ljava.lang.String;#6f496d9f, [Ljava.lang.String;#723279cf]
my list of String result
[fruit-Africa, Milk-Europ, Meat-Asia]
And in your question, you have:
I want to have this list of String in my result:
[fruit-africa,milk-Europ,Meat-Asia]
So, it looks like you already have the output you want for result. The only difference from the actual output is the lack of a space after each comma. If you don't want that space, then use joinToString to customize the output:
println(result.joinToString(",", "[", "]"))
As for:
[[Ljava.lang.String;#5b480cf9, [Ljava.lang.String;#6f496d9f, [Ljava.lang.String;#723279cf]
You see that output because arrays don't override the toString() function, and therefore use the default implementation. In Kotlin, you can use contentToString() to get similar output as you see when printing a List.
println(myArrayList.joinToString(", ", "[", "]") { it.contentToString() })
So, here is the updated code with the above changes:
fun main(args: Array<String>) {
val result: List<String>
val obj1 = arrayOf("fruit", "Mangue", "Africa")
val obj2 = arrayOf("Milk", "Soja", "Europ")
val obj3 = arrayOf("Meat", "cochon","Asia")
val myArrayList: ArrayList<Array<String>> = ArrayList<Array<String>>(3)
val myList: MutableList<Array<String>> = mutableListOf<Array<String>>()
myList.add(obj1)
myList.add(obj2)
myList.add(obj3)
myArrayList.addAll(myList)
result = myArrayList.stream().map{it -> ("${it[0]}-${it[2]}")}.toList()
println("ArrayList of objects :")
println(myArrayList.joinToString(", ", "[", "]") { it.contentToString() })
println("my list of String result")
println(result.joinToString(",", "[", "]"))
}
Which gives this output:
ArrayList of objects :
[[fruit, Mangue, Africa], [Milk, Soja, Europ], [Meat, cochon, Asia]]
my list of String result
[fruit-Africa,Milk-Europ,Meat-Asia]
Potential Improvements
With all that said, there are a few things you can simplify in your code:
This is a minor point, but since you don't use the args parameter you can actually omit it.
Your myList is not necessary; you can add your arrays directly to myArrayList.
Given the small number of elements in each array, and the small number of arrays, you can actually create the List<Array<String>> and populate it with a single listOf.
For variable types, you should prefer using List, the interface, rather than ArrayList, the implementation. This is known as "programming to an interface". Preferring List also means better use of listOf and mutableListOf, which are the idiomatic ways of creating lists in Kotlin.
You should prefer using List over arrays. In other words, create a List<List<String>> instead of a List<Array<String>>.
Lists do override the toString() method, providing readable output. Also, lists have better API support and work better with generics.
You don't need to use stream(). Kotlin provides many extension functions for arrays and Iterables, one of those being map which returns a List. Yes, these transformation functions are eagerly evaluated, unlike with streams, but given you're only performing one transfomration this doesn't really matter (in fact, the stream is likely less performant).
See kotlin.collections for the available built-in extension functions.
Given you want the first and last elements of each array, I would use first() and last().
Here is the simplified code (I added explicit types to make it clearer what the variables reference):
fun main() {
val lists: List<List<String>> = listOf(
listOf("Fruit", "Mangue", "Africa"),
listOf("Milk", "Soja", "Europe"),
listOf("Meat", "Cochon", "Asia")
)
println("List of lists of strings:")
println(lists)
val result: List<String> = lists.map { "${it.first()}-${it.last()}" }
println("Result:")
println(result)
}
Output:
List of Arrays:
[[Fruit, Mangue, Africa], [Milk, Soja, Europe], [Meat, Cochon, Asia]]
Result:
[Fruit-Africa, Milk-Europe, Meat-Asia]
I have an Array of [Long, Q] and would like to make a binary search on it. I tried below :
import scala.collection.Searching._
class Q (val b:Double, val a:Double)
val myArray = Array(5L -> new Q(1,2), 6L-> new Q(6,9), 7L-> new Q(7,6))
val i = myArray.search(6L).insertionPoint
but had this error
No implicit Ordering defined for Any
Unspecified value parameter ord.
I understand that I need to specify an odering rule for this collection Array[(Long,Q)] but can't figure this out myself.
Please help
Signature of search is search[B >: A](elem: B)(implicit ord: Ordering[B]). You've got an array of type [Long, Q]. So in order for the compiler to infer Ordering correctly, you'd have to invoke search like that:
myArray.search(6L-> q/*Q(6,9)*/)(Ordering.by(_._1)) //ordering by the first value in a tuple.
and what you're doing is: myArray.search(6L). If I understand correctly what you're trying to do, it's probably to find both value and position in the array.
You could solve it by using two separate data structures:
keys could be stored in the array, like this:
val myArray = Array(5L, 6L, 7L).toList
myArray.search(6L).insertionPoint
and if you'd need values, you could use map which would work as a dictionary:
val dictionary = Map(
5L -> new Q(1,2),
6L-> new Q(6,9),
7L-> new Q(7,6)
)
EDIT:
Actually, I noticed something like that would work:
val dummy = new Q(0,0) //any instance of Q
myArray.search(6L-> dummy)(Ordering.by(_._1)).insertionPoint //1
It works since for lookup of the insertion point Ordering is used and no equality test is performed.
Using JEXL, I am trying to initialize array and than adding elements into it, however below code gives me 'unsolvable property '0' error.
var abc=[];
abc[0]=5;
1) How can I initialize empty array and keep adding values in it?
2) Can I use it like List, where I do not need to specify size at the time of initialization ?
in JEXL syntax you can initialize objects with new function.
Other option is to add to context arraylist:
This is a working example with jexl2:
JexlEngine jexl = new JexlEngine();
String jexlExp = "var abc=new(\"java.util.ArrayList\", 1);abc[0]=5";
Expression e = jexl.createExpression( jexlExp );
List<Integer> abc = new ArrayList<>(1);
JexlContext jc = new MapContext();
//jc.set("abc", abc ); second option to add arraylist to context
Object o = e.evaluate(jc);
In JEXL, the syntax [] creates a Java array, not a List. As an array, it has a fixed size, so you cannot add values to it. However, JEXL 3.2 has a new syntax for creating an ArrayList literal. Basically, you add ... as the final element.
So in JEXL 3.2, your example could be written as:
var abc=[...];
abc.add(5);
See the JEXL literal syntax reference for more information.
In ssjs I have an array that contains jsonobjects. this array is stored in a scope variable and displayed in a repeat control:
<xp:repeat id="rptAssessors" value="#{sessionScope.tmpAssessors}" var="obj" indexVar="idx">
From the repeat control I would like to add the option to remove individual items from the array e.g. via onclick event on a button for each row:
<xp:eventHandler event="onclick" submit="true" refreshMode="partial" immediate="true" refreshId="dlgContent"> <xp:this.action> <xp:executeScript
script="#{javascript:removeAssessor(idx);}"> </xp:executeScript> </xp:this.action></xp:eventHandler>
My removeAssessor function looks as followed:
function removeAssessor(idx){
var jsonObjArr = sessionScope.get("tmpAssessors");
print("before elements " + jsonObjArr.length)
print(idx + 1)
jsonObjArr.splice(idx,1);
print("after elements " + jsonObjArr.length)
sessionScope.put("tmpAssessors",jsonObjArr);
}
I notice the splice() method does not work. I read on an xsnippet that this method does not work in SSJS and an alternative is posted as an xsnippet but this is for arrays containing strings
https://openntf.org/XSnippets.nsf/snippet.xsp?id=remove-an-entry-from-an-array-of-strings
Anyone can tell me how to remove an item from the array that is not a string?
Array.splice does work in SSJS, but not in the "inline way" you might be used to from CSJS: In CSJS the modification is done inline (no new array is created) and the removed elements are returned. In SSJS, the original array is not modified and the return value is a copy of the array excluding the spliced elements.
If you replace jsonObjArr.splice(idx,1); with jsonObjArr=jsonObjArr.splice(idx,1); your code should work fine.
So I have an array: var pics:[UIImage?] = []
when I type: pics.removeLast()
XCode returns me the yellow triangle with error "Expression of type 'UIImage?' is unused"
How to remove the last item without errors ?
As you can see from the method declaration removeLast() returns an Iterator.Element. To silent the warning you can use _.
Example: _ = pics.removeLast()