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.
Related
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]
Let's say I have an array of strings and I want to get a list with objects that match, such as:
var locales=Locale.getAvailableLocales()
val filtered = locales.filter { l-> l.language=="en" }
except, instead of a single value I want to compare it with another list, like:
val lang = listOf("en", "fr", "es")
How do I do that? I'm looking for a one-liner solution without any loops. Thanks!
Like this
var locales = Locale.getAvailableLocales()
val filtered = locales.filter { l -> lang.contains(l.language)}
As pointed out in comments, you can skip naming the parameter to the lambda, and use it keyword to have either of the following:
val filtered1 = locales.filter{ lang.contains(it.language) }
val filtered2 = locales.filter{ it.language in lang }
Just remember to have a suitable data structure for the languages, so that the contains() method has low time complexity like a Set.
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.
I have an array loaded in, and been playing around in the REPL but can't seem to get this to work.
My array looks like this:
record_id|string|FALSE|1|
offer_id|decimal|FALSE|1|1,1
decision_id|decimal|FALSE|1|1,1
offer_type_cd|integer|FALSE|1|1,1
promo_id|decimal|FALSE|1|1,1
pymt_method_type_cd|decimal|FALSE|1|1,1
cs_result_id|decimal|FALSE|1|1,1
cs_result_usage_type_cd|decimal|FALSE|1|1,1
rate_index_type_cd|decimal|FALSE|1|1,1
sub_product_id|decimal|FALSE|1|1,1
campaign_id|decimal|FALSE|1|1,1
When I run my command:
for(i <- 0 until schema.length){
val convert = schema(i).toString;
convert.split('|').drop(2);
println(convert);
}
It won't drop anything. It also is not splitting it on the |
Strings are immutable, and so split and drop don't mutate the string - they return a new one.
You need to capture the result in a new val
val split = convert.split('|').drop(2);
println(split.mkString(" "));
Consider also defining a lambda function for mapping each item in the array, where intermediate results are passed on with the function,
val res = schema.map(s => s.toString.split('|').drop(2))
I’m new to Swift and have been having some troubles figuring out some aspects of Arrays and Dictionaries.
I have an array of dictionaries, for which I have used Type Aliases - e.g.
typealias myDicts = Dictionary<String, Double>
var myArray : [myDicts] = [
["id":0,
"lat”:55.555555,
"lng”:-55.555555,
"distance":0],
["id":1,
"lat": 44.444444,
"lng”:-44.444444,
"distance":0]
]
I then want to iterate through the dictionaries in the array and change the “distance” key value. I did it like this:
for dict:myDicts in myArray {
dict["distance"] = 5
}
Or even specifically making sure 5 is a double with many different approaches including e.g.
for dict:myDicts in myArray {
let numberFive : Double = 5
dict["distance"] = numberFive
}
All my attempts cause an error:
#lvalue $T5' is not identical to '(String, Double)
It seems to be acting as if the Dictionaries inside were immutable “let” rather than “var”. So I randomly tried this:
for (var dict:myDicts) in myArray {
dict["distance"] = 5
}
This removes the error and the key is indeed assigned 5 within the for loop, but this doesn't seem to actually modify the array itself in the long run. What am I doing wrong?
The implicitly declared variable in a for-in loop in Swift is constant by default (let), that's why you can't modify it directly in the loop.
The for-in documentation has this:
for index in 1...5 {
println("\(index) times 5 is \(index * 5)")
}
In the example above, index is a constant whose value is automatically
set at the start of each iteration of the loop. As such, it does not
have to be declared before it is used. It is implicitly declared
simply by its inclusion in the loop declaration, without the need for
a let declaration keyword.
As you've discovered, you can make it a variable by explicitly declaring it with var. However, in this case, you're trying to modify a dictionary which is a struct and, therefore, a value type and it is copied on assignment. When you do dict["distance"] = 5 you're actually modifying a copy of the dictionary and not the original stored in the array.
You can still modify the dictionary in the array, you just have to do it directly by looping over the array by index:
for index in 0..<myArray.count {
myArray[index]["distance"] = 5
}
This way, you're sure to by modifying the original dictionary instead of a copy of it.
That being said, #matt's suggestion to use a custom class is usually the best route to take.
You're not doing anything wrong. That's how Swift works. You have two options:
Use NSMutableDictionary rather than a Swift dictionary.
Use a custom class instead of a dictionary. In a way this is a better solution anyway because it's what you should have been doing all along in a situation where all the dictionaries have the same structure.
The "custom class" I'm talking about would be a mere "value class", a bundle of properties. This was kind of a pain to make in Objective-C, but in Swift it's trivial, so I now do this a lot. The thing is that you can stick the class definition for your custom class anywhere; it doesn't need a file of its own, and of course in Swift you don't have the interface/implementation foo to grapple with, let alone memory management and other stuff. So this is just a few lines of code that you can stick right in with the code you've already got.
Here's an example from my own code:
class Model {
var task : NSURLSessionTask!
var im : UIImage!
var text : String!
var picurl : String!
}
We then have an array of Model and away we go.
So, in your example:
class MyDict : NSObject {
var id = 0.0
var lat = 0.0
var lng = 0.0
var distance = 0.0
}
var myArray = [MyDict]()
let d1 = MyDict()
d1.id = 0
d1.lat = 55.55
d1.lng = -55.55
d1.distance = 0
let d2 = MyDict()
d2.id = 0
d2.lat = 44.44
d2.lng = -44.44
d2.distance = 0
myArray = [d1,d2]
// now we come to the actual heart of the matter
for d in myArray {
d.distance = 5
}
println(myArray[0].distance) // it worked
println(myArray[1].distance) // it worked
Yes, the dictionary retrieved in the loop is immutable, hence you cannot change.
I'm afraid your last attempt just creates a mutable copy of it.
One possible workaround is to use NSMutableDictionary:
typealias myDicts = NSMutableDictionary
Have a class wrapper for the Swift dictionary or array.
class MyDictionary: NSObject {
var data : Dictionary<String,Any>!
init(_ data: Dictionary<String,Any>) {
self.data = data
}}
MyDictionary.data