I'm using lambda expression and trying convert into uint while adding into the Hashset. Here what I'm doing:
HashSet<uint> LeadsInSession = new HashSet<uint>();
if (HttpContext.Current.Session["Category_SelectedLeadIds"] != null)
{
Dictionary<LeadPurchase.CategoryLeadSearch, List<string>> toRemoveLeadsIDs =
(Dictionary<LeadPurchase.CategoryLeadSearch, List<string>>)HttpContext.Current.Session["Category_SelectedLeadIds"];
LeadPurchase.CategoryLeadSearch searches = (LeadPurchase.CategoryLeadSearch)HttpContext.Current.Session["searches"];
var toAdd = toRemoveLeadsIDs.Where(Pair => Pair.Key.VerticalID == searches.VerticalID)
.Select(Pair => Pair.Value)
.ToList();
foreach (var lead in toAdd)
LeadsInSession.Add(lead);// I need to convert lead into uint. Convert.ToUInt32() didn't work here.
}
Any way around?
Your problem is that toRemoveLoasIOs is a dictionary with a value type of List<string>. Therefore toAdd will be IEnumerable<List<string>>, and thus lead is List<string> which, quite reasonably will not convert to uint.
You need to iterate over both toAdd and, an inner loop, over lead and then you have the individual strings to convert. Something like:
foreach (var lead in toAdd) {
foreach (string value in lead) {
uint u;
if (UInt32.TryParse(value, out u)) {
LeadsInSession.Add(u);
}
}
}
Did you Try ?
LeadPurchase.CategoryLeadSearch searches
= (LeadPurchase.CategoryLeadSearch) HttpContext.Current.Session["searches"];
var toAdd = toRemoveLeadsIDs.Where(Pair => Pair.Key.VerticalID == searches.VerticalID)
.Select(Pair => (uint)Pair.Value)
.ToList<uint>();
foreach (var lead in toAdd)
LeadsInSession.Add(lead);
}
Related
Is there a way to sort something like:
List<String> hi = ['1hi', '2hi','5hi', '3hi', '4hi'];
to this?
['1hi', '2hi','3hi', '4hi', '5hi']
Just calling List<String>.sort() by itself will do a lexicographic sort. That is, your strings will be sorted in character code order, and '10' will be sorted before '2'. That usually isn't expected.
A lexicographic sort will work if your numbers have leading 0s to ensure that all numbers have the same number of digits. However, if the number of digits is variable, you will need to parse the values of the numbers for sorting. A more general approach is to provide a callback to .sort() to tell it how to determine the relative ordering of two items.
Luckily, package:collection has a compareNatural function that can do this for you:
import 'package:collection/collection.dart';
List<String> hi = ['1hi', '2hi','5hi', '3hi', '4hi'];
hi.sort(compareNatural);
If your situation is a bit more complicated and compareNatural doesn't do what you want, a more general approach is to make the .sort() callback do parsing itself, such as via a regular expression:
/// Returns the integer prefix from a string.
///
/// Returns null if no integer prefix is found.
int parseIntPrefix(String s) {
var re = RegExp(r'(-?[0-9]+).*');
var match = re.firstMatch(s);
if (match == null) {
return null;
}
return int.parse(match.group(1));
}
int compareIntPrefixes(String a, String b) {
var aValue = parseIntPrefix(a);
var bValue = parseIntPrefix(b);
if (aValue != null && bValue != null) {
return aValue - bValue;
}
if (aValue == null && bValue == null) {
// If neither string has an integer prefix, sort the strings lexically.
return a.compareTo(b);
}
// Sort strings with integer prefixes before strings without.
if (aValue == null) {
return 1;
} else {
return -1;
}
}
void main() {
List<String> hi = ['1hi', '2hi','5hi', '3hi', '4hi'];
hi.sort(compareIntPrefixes);
}
You can sort the list like this:
hi.sort();
(because numbers sort before letters in its implementation)
I created a function that recieves input and compare it to a list, when find a match it return the match, in this case this match is the attribute of a class that i created.
I understand that the problem is with the return statement, so in the beginning of the function I declare the return as "Any", further more than that I'm kinda lost.
The error is this: A 'return' expression required in a function with a block body ('{...}')
class Class1(var self: String)
var test_class = Class1("")
fun giver(){
test_class.self = "Anything"
}
class Funciones(){
fun match_finder(texto: String): Any{
var lista = listOf<String>(test_class.self)
var lista_de_listas = listOf<String>("test_class.self")
var count = -1
for (i in lista_de_listas){
count = count + 1
if (texto == i){
lista_de_listas = lista
var variable = lista_de_listas[count]
return variable
}
}
}
}
fun main(){
giver()
var x = "test_class.self"
var funcion = Funciones()
var y = funcion.match_finder(x)
println(y)
}
To explain you what the problem is, let's consider the following code:
class MyClass {
fun doSomething(): String {
val numbers = listOf(1, 2, 3)
for (number in numbers) {
if (number % 2 == 0) {
return "There is at least one even number in the list"
}
}
}
}
If you try compiling it you'll get the same error message as in your question: A 'return' expression required in a function with a block body ('{...}'). Why is that?
Well, we defined a function doSomething returning a String (it could be any other type) but we're returning a result only if the list of numbers contains at least one even number. What should it return if there's no even number? The compiler doesn't know that (how could it know?), so it prompts us that message. We can fix the code by returning a value or by throwing an exception:
class MyClass {
fun doSomething(): String {
val numbers = listOf(1, 2, 3)
for (number in numbers) {
if (number % 2 == 0) {
return "There is at least one even number in the list"
}
}
// return something if the list doesn't contain any even number
return "There is no even number in the list"
}
}
The same logic applies to your original code: what should the function return if there is no i such that texto == i?
Please also note that the solution you proposed may be syntactically correct - meaning it compiles correctly - but will probably do something unexpected. The for loop is useless since the if/else statement will always cause the function to return during the first iteration, so the value "There is no match" could be returned even if a match actually exists later in the list.
I searched online, if someone has the same problem, the correct code is as follows:
class Funciones(){
fun match_finder(texto: String): Any{
var lista = listOf<String>(test_class.self)
var lista_de_listas = listOf<String>("test_class.self")
var count = -1
var variable = " "
for (i in lista_de_listas){
count = count + 1
if (texto == i){
lista_de_listas = lista
var variable = lista_de_listas[count]
return variable
} else {
return "There is no match"
}
}
return variable
}
}
I'm not seeing anything ever get returned by the scan. I know it's because the mutableList gets returned right away, but how do I block the return until the time expires?
Basically, all I want to do is fill up the mutable list for as long as the take() permits then return that mutableList to the calling function.
This is what I have tried.
private val timeoutScheduler: Scheduler = Schedulers.computation()
fun scanForAllDevicesStartingWith(devicePrefix: String): List<String> {
Log.d(TAG, "Scanning for devices starting with $devicePrefix")
val mutableList = mutableListOf<String>()
val result = scanForDevices()
.take(3, TimeUnit.SECONDS, timeoutScheduler)
.subscribe { scanResult ->
val name = scanResult.bleDevice.name
Logger.d(TAG, "Potential device named $name found")
if(name != null) {
if(name.startsWith(prefix = devicePrefix)) {
Logger.d(TAG, "Match found $name")
mutableList.plus(name)
}
}
}
return mutableList
}
private fun scanForDevices(): Observable<ScanResult>
= rxBleClient.scanBleDevices(
ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
.setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES)
.build(),
ScanFilter.Builder()
.build())
}
OK, here it is boiled down for the next person who wants to do this kind of thing. In Rx, they have Singles which are Observables that just emit one value. In my case I needed a list of String values, so just need to use a Single of type List of type String. That gets just one element emitted that happens to be a list of Strings. The code looks like this...
fun returnAllDevicesStartingWith(devicePrefix: String): Single<List<String>> {
return scanForDevices()
.take(3, TimeUnit.SECONDS, timeoutScheduler)
.map { it.bleDevice.name }
.filter { it.startsWith(devicePrefix) }
.toList()
}
The function that calls it (written in Java instead of Kotlin) looks like this:
List<String> devices = bleUtility.returnAllDevicesStartingWith(prefix).blockingGet();
I tested it using a mocked function like this:
//Begin test code
var emittedList: List<String> = listOf("dev1-1", "dev1-2", "dev2-1", "dev2-2", "dev3-1", "dev3-2")
private fun scanForRoomDevices(): Observable<FoundDevice> = Observable
.intervalRange(0, emittedList.size.toLong(), 0, 1, TimeUnit.SECONDS, timeoutScheduler)
.map { index -> FoundDevice(emittedList[index.toInt()], BleDevice(emittedList[index.toInt()])) }
data class FoundDevice(val controllerId: String, val bleDevice: BleDevice)
data class BleDevice(val name: String)
Hope this helps others.
For exercise I'm trying to implement a LinkedList in Scala.
Main problem is about Null reference.
But first some code:
class Node(xkey: String, xnext: Option[Node], xinfo: Int) {
val key: String = xkey;
var next = xnext.getOrElse(None);
var info: Int = xinfo;
def this(xkey: String, xinfo: Int) {
this(xkey, None, xinfo);
}
def this(xkey: String) {
this(xkey, None, -1);
}
#Override
override def toString: String = key + ":" + info
}
At this point, I'm already concerned about things.
I declare xnext in construct as a Option[Node], because the tail in this linkedList does not have a next.
In my first try, it was just a Node, but had problem with null object because compilator just told me that "null can't cast to Node" (or something like that, I do not remember now) - And so I switch to this Option.
But, is it ok? Because, you know, for me next should be a Node, not a Option, otherwise, I don't know, in the linkedList how to reference to next Node.
Whatever, second class (i.e. my Linked List)
class LinkedNode {
private var first: Option[Node] = None;
private var last: Option[Node] = None;
def addNode(newNode: Node) = {
if (first == null) {
first = Some(newNode);
last = Some(newNode);
first.next = last;
}
else {
last.next = newNode;
newNode.next = null;
last = newNode
}
}
def size(): Long = {
var currentNode : = first;
var size = 0L;
while (currentNode != null) {
size+=1;
currentNode = currentNode.next;
}
size
}
def findNodeByKey(key: String) : Node = {
var currentNode = first;
while(currentNode != null) {
if (currentNode.key.equals(key))
currentNode
else {
currentNode = currentNode.next;
}
}
currentNode;
}
def delNodeByKey(key : String) : Boolean = {
var currentNode = first;
var previousNode = first;
while(currentNode != null) {
if (currentNode.key.equals(key)) {
previousNode = currentNode.next;
return true;
}
previousNode = currentNode;
currentNode = currentNode.next;
}
return false;
}
}
And nothing. I'm already block to my constructor because first and last.
How should I declare them? Node? Or Option[Node]?
Problems are also in Add method.
When I add a node, I want to add a Node object, not an Option[Node].
And I don't get how to achieve things I want with all Option, Some and None classes.
I know I should not be so vague with my request, but any help?
P.S. I've already read this Q/A and it didn't help me
At this point, I'm already concerned about things. I declare xnext in construct as a Option[Node], because the tail in this linkedList does not have a next.
[...]
But, is ok? because, you know, for me next should be a Node, not a Option, otherwise, I don't know, in the linkedList how to reference to next Node.
This is a good solution to replacing null, which you definitely want to do to prevent null-pointer exceptions and the like. An Option[Node] is simply a Node wrapped in a container (or None). You can check whether or not it has a value with isEmpty or get its value with get (which will throw an exception if the Option is empty).
The only difference to null, as you'd use it in Java, is that you need to check if it isEmpty instead of checking for null, and that you need to unwrap (option.get) it explicitly when you're sure that it is not None.
A more paradigmatic (scala-typical) way of retrieving the value from an option is pattern matching:
option match {
case Some(x) => println(x)
case None => println("Whoops, no value :(")
}
Regarding your other questions, they are indeed a little vague.
How should I declere them? Node? or Option[Node]?
Use Option[Node] if the possibility exists that there's no value for the variable (i.e., if you'd set it to null sometimes in Java).
When I add a node, I want to add a Node object, not a Option[Node].
No, you want to add an Option[Node] internally, because you will need to check later on if a node is set or not. In Scala it is preferrable to do this via Option[Node].isEmpty compared to setting things to null. You're already doing this in some parts of your code (e.g., addNode), where you do Some(newNode) (I'd call this "wrapping the node in an Option", but I'm not entirely sure if that's the correct terminology).
And I don't get how to achieve things I want with all Option, Some and None class.
What you're doing in your addNode does seem correct to a degree, but you somehow try to use null again in the else branch. What about:
// We don't need Option[Node] for the parameter, because there
// _must_ be a Node value to be added
def addNode(newNode: Node) = {
if (first.isEmpty) {
first = Some(newNode)
last = Some(newNode)
first.next = last
} else {
newNode.next = None
last.next = Some(newNode)
last = Some(newNode)
}
}
(I didn't run that code, nor did I do an thorough check of your logic)
i am having the following for loop,
for (key, value) in changedDataDictionary {
// here i want to identify last key and value
}
I want to identify the execution of last object/ completion of the for loop
It may be very silly question, but i dont have any idea about that.
Thanks in advance.
This will work in general
var index: Int = 0
for (key, value) in changedDataDictionary {
index += 1;
if (index == changedDataDictionary.count) {
// do something
}
}
Note that a dictionary doesn't have a defined order so the last element will always be a different one and usually there is a better solution than using a tracking index.
If you just want to identify last key and element, you can also:
var lastKey: KeyType? = nil
var lastElement ValueType? = nil
for (key, value) in changedDataDictionary {
lastKey = key;
lastValue = value;
}
// do something with last key and value