I need to write somehow a function, that aggregates results in a list.
I'm working with an Order dto (java class)
public class Order {
private Long orderId;
private String description;
...
}
I have two APIs, the one that return orders and the other one that returns suborders. So i retrieve all orders and get all suborders in a loop by predefined ids:
// for example i have a predefined list of order id's
List<Long> orderIds = listOf(1L, 2L, 3L, 4L, 5L)
val allOrders = orderIds.map {
// at first i retrieve an order
val order = orderService.getOrderById(it.orderId)
// then i get a list of suborders
val suborders = suborderService.getSubordersByOrderId(it.orderId)
// ?
}
How can i combine order (Order) and suborders (List) to a list of Order and then all the elements of nested list into a single list?
I think flatMap is what you want:
val allOrders: List<Order> = orderIds.flatMap {
val order = orderService.getOrderById(it)
val suborders = suborderService.getSubordersByOrderId(it)
suborders + order
}
It flatten all the items of the returned list into one single list altogether.
Related
I have 2 Lists (uid and url) that are growable, and I need to set the first List as the key and the second as value. At some point, i'll have a 3rd List (randomUids) which will be keys and will print out the corresponding values. Here is the example code:
List<String> uid = ["uid1", "uid2","uid3","uid4"]; //Lists will grow larger after a while
List<String> url = ["url1","url2","url3","url4"];
List<String> randomUids = ["uid4", "uid2"];
When I try:
Map<List, List> mapKeyValue = Map();
mapKeyValue[uid] = url;
print( uid.contains(randomUids));
I get a false. Also, the print returns uid and url Lists as 2 long indices instead of separate Strings. How can I iterate the List so that url.contains(randomUids) is true. Also how can I print out the values of randomUids.
When I try:
print( uid.contains(randomUids));
I get a false.
Your code asks if uid (a List of Strings) contains randomUids (another List of Strings). It returns false because uid's elements are not Lists; they're Strings.
Presuming that you want the nth element of uid to correspond to the nth element of url, and you can guarantee that uid.length == url.length, you can construct a Map of UIDs to URLs:
assert(uid.length == url.length);
var uidMap = <String, String>{
for (var i = 0; i < uid.length; i += 1)
uid[i]: url[i],
};
And then you can iterate over randomUids and do lookups:
for (var uid in randomUids) {
if (uidMap.containsKey(uid)) {
print(uidMap[uid]);
}
}
I'm looking for a simplest way to sort list based on given value instead of using two list.
Example I have list [a,b,c,d], with a given value d,I can sort it like this:
But if I have an object list, how can I sort it based on given value?
Example
List<ABC> list = [{fid:1,name:"a"},{fid:2,name:"b"},{fid:3,name:"c"},{fid:4,name:"d"}]
I have value 3. I want to sort the list become
List<ABC> list = [{fid:3,name:"c"},{fid:1,name:"A"},{fid:2,name:"b"},{fid:4,name:"d"},{fid:4,name:"d"}]
You just need to perform custom sorting here, rest of the things will remain same.
List list = [{"fid":1,"name":"z"},{"fid":10,"name":"b"},{"fid":5,"name":"c"},{"fid":4,"name":"d"}];
list.sort((a,b)=> a["fid"].compareTo(b["fid"]));
int fidIndex=4;
int indexToRemove=list.indexWhere((element) => element["fid"]==fidIndex);
Map<String,dynamic> removedItem= list.removeAt(indexToRemove);
list.insert(0,removedItem);
print(list);
You can sort list using comparator:
const list = [{fid:1,name:"a"},{fid:2,name:"b"},{fid:3,name:"c"},{fid:4,name:"d"}]
const fixedFid = 3
const sortedList = list.sort( (item1, item2) => {
if (item1.fid === fixedFid){
return -1
}
if (item2.fid == fixedFid){
return 1
}
return item1.fid.localeCompare(item2.fid)
})
I have two Lists of objects that both implement an interface, but are otherwise unrelated. How can I create a new collection of objects containing only the objects of one of the lists that match a value in the other list?
Obviously I could use a for loop & do this manually, but I'd like to know how I can do this using Kotlin's standard library collection filtering functions.
So here's an example:
interface Ids
{
val id: Int
}
data class A(override val id: Int, val name: String) : Ids
data class B(override val id: Int, val timestamp: Long) : Ids
fun main(args: Array<String>) {
val a1 = A(1, "Steve")
val a2 = A(2, "Ed")
val aCol = listOf(a1, a2)
val b2 = B(2, 12345)
val b3 = B(3, 67890)
val bCol = listOf(b2, b3)
val matches = mutableListOf<B>()
// This is where I'm stuck.
// I want to filter bCol using objects from aCol as a filter.
// The result should be that matches contains only a single object: b2
// because bCol[0].id == aCol[1].id
// I'm guessing I need to start with something like this:
bCol.filterTo(matches) { ??? }
}
A straightforward approach would be to search aCol for an object with the same id for each b in bCol:
bCol.filter { b -> aCol.any { a -> a.id == b.id } }
However that may become too slow if your lists are big enough.
To make it more scalable you can first build a set of all ids in aCol:
val aColIds = aCol.map { it.id }.toSet()
And then use Set.contains method to determine whether b.id is in aColIds:
bCol.filter { it.id in aColIds }
// or equivalent
bCol.filter { aColIds.contains(it.id) }
Please see I want list employee objects. So I have below two options.
List<Tuple<int, string, string, string>>
List<Employee>where Employee is class contains 4 properties.
My doubt is what should I use(tuple or list of employee object?
If it is List<Employee> then in which scenario I should use List<Tuple<int, string, ...>>.
You should not use tuples unless you are doing some sort of arithmetic operation where tuple would be an acceptable and widely understood method of supplying values. Tuples make it a maintenance nightmare for anyone who is not familiar with your process as you built it.
Edit: Think about the difference between seeing:
var employeeList = DAL.getEmployees();
var activeEmployees = employeeList.Where(employee => employee.IsActive);
vs
var employeeTuple = DAL.getEmployees();
var activeEmployees = employeeTuple.Where(employee => employee.Item3);
In the second example, I know THAT you created an active employee list, but I don't know HOW you did it.
That's rather obvious. If you already have the Employee class then using List<Employee> is straightforward:
List<Employee> list = new List<Employee>();
list.Add( e );
...
Employee e = list.Where( i => i.Name == "John" ).FirstOrDefault();
whereas using List<Tuple<...>> is at least cumbersome:
List<Tuple<....>> list = new List<Tuple<....>>();
list.Add( new Tuple<...>( e.Name, e.Surname, e.Whateverelse, e.YetAnother ) );
...
// retrieve the tuple
var tuple = list.Where( i => i.Item1 == "John" );
// make Employee out of it
Employee e = new Employee( e.Item1, e.Item2, e.Item3, e.Item4 );
I'm looking every where on the web (dart website, stackoverflow, forums, etc), and I can't find my answer.
So there is my problem: I need to write a function, that print a random sort of a list, witch is provided as an argument. : In dart as well.
I try with maps, with Sets, with list ... I try the method with assert, with sort, I look at random method with Math on dart librabry ... nothing can do what I wana do.
Can some one help me with this?
Here some draft:
var element03 = query('#exercice03');
var uneliste03 = {'01':'Jean', '02':'Maximilien', '03':'Brigitte', '04':'Sonia', '05':'Jean-Pierre', '06':'Sandra'};
var alluneliste03 = new Map.from(uneliste03);
assert(uneliste03 != alluneliste03);
print(alluneliste03);
var ingredients = new Set();
ingredients.addAll(['Jean', 'Maximilien', 'Brigitte', 'Sonia', 'Jean-Pierre', 'Sandra']);
var alluneliste03 = new Map.from(ingredients);
assert(ingredients != alluneliste03);
//assert(ingredients.length == 4);
print(ingredients);
var fruits = <String>['bananas', 'apples', 'oranges'];
fruits.sort();
print(fruits);
There is a shuffle method in the List class. The methods shuffles the list in place. You can call it without an argument or provide a random number generator instance:
var list = ['a', 'b', 'c', 'd'];
list.shuffle();
print('$list');
The collection package comes with a shuffle function/extension that also supports specifying a sub range to shuffle:
void shuffle (
List list,
[int start = 0,
int end]
)
Here is a basic shuffle function. Note that the resulting shuffle is not cryptographically strong. It uses Dart's Random class, which produces pseudorandom data not suitable for cryptographic use.
import 'dart:math';
List shuffle(List items) {
var random = new Random();
// Go through all elements.
for (var i = items.length - 1; i > 0; i--) {
// Pick a pseudorandom number according to the list length
var n = random.nextInt(i + 1);
var temp = items[i];
items[i] = items[n];
items[n] = temp;
}
return items;
}
main() {
var items = ['foo', 'bar', 'baz', 'qux'];
print(shuffle(items));
}
You can use shuffle() with 2 dots like Vinoth Vino said.
List cities = ["Ankara","London","Paris"];
List mixed = cities..shuffle();
print(mixed);
// [London, Paris, Ankara]