I've been trying to implement a dropdown menu but i wanted to utilise the key data maps have.
a simple example of the data i want to process
List<String> Test = [ Test1,Test2,Test3,Test4 ];
Map<int,String> Test2 = { 0 : Test1 , 1 : Test2, 2: Test3, 3:Test4};
my list version:
EM.DigitalFunctionList.map((String item) => DropdownMenuItem<String>(
value: item,
child: Text("$item and ${item.indexOf($item)}"),
),).toList(),
),
this at the moment returns a "item x and 0 " for all values so im not too sure why thats happened but
Link
it states to get an index from a list you have to convert it to a map, so im a tad stumped
Change it to this is you are trying to get the the index of item in your parent list
EM.DigitalFunctionList.indexOf($item)
Related
I am new to Esper and i am working on Storm-Esper collaboration.Through my main class,i send queries to a bolt which contains esper while the esper-bolt sends the tuple which contain the results to a printer bolt.My problem is that,although the result of a query is correct as for the values,the attribute values are not in the correct order.For example,i have a query which selects attributes from a pilot's table: name,surname,airline and i should have the result in the same order.However i get:name,airline,surname.I have tried everything concerning group by and order by.I suppose it must be an Esper's fault when creating the event's map which contains the attributes-values.I paste the main class code and the esper bolt code where the map is processed.Any idea why is that happening is most welcome!
**mainclass**
.addStatements(("insert into pilotStream " +
"select * " +
"from Log.win:time(120 second) A "))
.addStatements(("insert into employeeStream " +
"select * " +
"from Emp.win:time(120 second) A "))
.addStatements(("insert into CombinedEvent "+
"select tick.pilotName as p_name , " +
"tick.pilotSurname as p_surname , " +
"tick.airline as p_airline " +
"from pilotStream.win:time(120 second) as tick, " +
"employeeStream.win:time(120 second) as rom "+
"where tick.airline = rom.employeeAirline "+
))
**espebolt**
Map<String, Object> emap = (Map<String, Object>) newEvent.getUnderlying();
String Event_name = newEvent.getEventType().getName();
//System.out.println(Event_name);
for (Map.Entry<String, Object> entry : emap.entrySet()) {
// String key = entry.getKey();
String val = String.valueOf(entry.getValue()) ;
//System.out.println(key+" :"+val);
//System.out.println(val);
values.add(val);
}
collector.emit(Event_name, toTuple(newEvent, values, false));
values.removeAll(values);
The result should be : source: Esper-Print:2, stream: CombinedEvent, id: {}, [John, Snow, Lufthansa]
Instead,i get:source: Esper-Print:2, stream: CombinedEvent, id: {}, [John, Lufthansa, Snow]
P.S.The toTuple functions simply gets the values of the attributes through the values list of strings and puts them into a tuple which is emitted to printerbolt.In the espebolt code there is some printing in comments which helped me see that the problem is in the map which esper creates internally.
By default Esper generates Map events. This can be changed into object-array events when setting a configuration or with annotations. Map events use "HashMap" and not "LinkedHashMap". The "HashMap" is not ordered when iterating the key-value pairs but takes much less memory. Object-array is ordered. For ordered access to Map events there is the "EventType" that you can get from a statement which returns you the property names in order.
I have to generate a number based on a given start , end and step and insert it into an array , for eg , Start = 10 , end = 30 , step = 5 , then
my array should be [10,15,20,25,30] , I am able to achieve this by the below method
for var index in stride(from: start, through: end, by: step) {
self.myArray.append(self.getElement(number: index))
}
But I keep getting a warning in xCode as variable index was never mutated , and if I change the var index to let index then I get a compilation error as "let pattern cannot appear nested in an already immutable context'.
Any idea how to suppress this warning in Swift 3?
Just delete var entirely. for index in...
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 have 2 immutable case classes A(source, key, value) and B(source, key, value)
I want to add A over B in such a way when 'source' and 'key' doesn't exist, to be added from A to the B and when 'source' and 'key' exist to replace the value from B with the one from A. The same way 'merge_array' function from php works on a multidimensional array.
I tried with 'A.union(B).groupBy(.key)' and then 'groupBy(.source)' and get the 1st value. But then I realized that I can never be sure that first value will always be the value of A.
I'm quite new to scala and I really ran out of ideas how I could do this from a functional immutable point of view.
Anyone has any idea how I could do this?
Thank you
Edit:
case class TranslationValue(source: String, key: String, value: String)
def main(args:Array[String]):Unit = {
println(merge(data1.toSet, data2.toSet))
}
def merge(a: Set[TranslationValue], b: Set[TranslationValue]) = {
a.union(b).groupBy(_.key).flatMap{ case (s, v) =>
v.groupBy(_.source).flatMap{case (s1, v1) => {
for (res <- 0 to 0) yield v1.head
}
}
}
}
Example
data1 has this data
Set(
TranslationValue(messages,No,No),
TranslationValue(messages,OrdRef,Order Reference),
TranslationValue(messages,OrdId,Order Id)
)
data2 has this data
Set(
TranslationValue(messages,No,No),
TranslationValue(messages,OrdRef,OrderRef)
TranslationValue(messages,Name,Name)
)
putting data1 over data2 I want to obtain
List(
TranslationValue(messages,No,No),
TranslationValue(messages,OrdRef,Order Reference),
TranslationValue(messages,OrdId,Order Id)
TranslationValue(messages,Name,Name)
)
I know that what I do can be done better, but like I said, I'm learning :)
you can group in one go:
def merge(a: Seq[TranslationValue], b: Seq[TranslationValue]) = {
a.union(b).groupBy(t=>(t.key,t.source)).map(c=>c._2.head)
}
i think you could also override the equals method for TranslationValue so that two translation values are equal when source and key are the same(the hashcode method has also to be overridden). Then a.union(b) would be enough.
edit:
It seems Set doesnt guarantee order of items(Scala: Can I rely on the order of items in a Set?), but a seq should.
I am seeing a problem with some Scala 2.7.7 code I'm working on, that should not happen if it the equivalent was written in Java. Loosely, the code goes creates a bunch of card players and assigns them to tables.
class Player(val playerNumber : Int)
class Table (val tableNumber : Int) {
var players : List[Player] = List()
def registerPlayer(player : Player) {
println("Registering player " + player.playerNumber + " on table " + tableNumber)
players = player :: players
}
}
object PlayerRegistrar {
def assignPlayersToTables(playSamplesToExecute : Int, playersPerTable:Int) = {
val numTables = playSamplesToExecute / playersPerTable
val tables = (1 to numTables).map(new Table(_))
assert(tables.size == numTables)
(0 until playSamplesToExecute).foreach {playSample =>
val tableNumber : Int = playSample % numTables
tables(tableNumber).registerPlayer(new Player(playSample))
}
tables
}
}
The PlayerRegistrar assigns a number of players between tables. First, it works out how many tables it will need to break up the players between and creates a List of them.
Then in the second part of the code, it works out which table a player should be assigned to, pulls that table from the list and registers a new player on that table.
The list of players on a table is a var, and is overwritten each time registerPlayer() is called. I have checked that this works correctly through a simple TestNG test:
#Test def testRegisterPlayer_multiplePlayers() {
val table = new Table(1)
(1 to 10).foreach { playerNumber =>
val player = new Player(playerNumber)
table.registerPlayer(player)
assert(table.players.contains(player))
assert(table.players.length == playerNumber)
}
}
I then test the table assignment:
#Test def testAssignPlayerToTables_1table() = {
val tables = PlayerRegistrar.assignPlayersToTables(10, 10)
assertEquals(tables.length, 1)
assertEquals(tables(0).players.length, 10)
}
The test fails with "expected:<10> but was:<0>". I've been scratching my head, but can't work out why registerPlayer() isn't mutating the table in the list. Any help would be appreciated.
The reason is that in the assignPlayersToTables method, you are creating a new Table object. You can confirm this by adding some debugging into the loop:
val tableNumber : Int = playSample % numTables
println(tables(tableNumber))
tables(tableNumber).registerPlayer(new Player(playSample))
Yielding something like:
Main$$anon$1$Table#5c73a7ab
Registering player 0 on table 1
Main$$anon$1$Table#21f8c6df
Registering player 1 on table 1
Main$$anon$1$Table#53c86be5
Registering player 2 on table 1
Note how the memory address of the table is different for each call.
The reason for this behaviour is that a Range is non-strict in Scala (until Scala 2.8, anyway). This means that the call to the range is not evaluated until it's needed. So you think you're getting back a list of Table objects, but actually you're getting back a range which is evaluated (instantiating a new Table object) each time you call it. Again, you can confirm this by adding some debugging:
val tables = (1 to numTables).map(new Table(_))
println(tables)
Which gives you:
RangeM(Main$$anon$1$Table#5492bbba)
To do what you want, add a toList to the end:
val tables = (1 to numTables).map(new Table(_)).toList
val tables = (1 to numTables).map(new Table(_))
This line seems to be causing all the trouble - mapping over 1 to n gives you a RandomAccessSeq.Projection, and to be honest, I don't know how exactly they work, but a bit less clever initialising technique does the job.
var tables: Array[Table] = new Array(numTables)
for (i <- 0 to numTables) tables(i) = new Table(i)
Using the first initialisation method I wasn't able to change the objects (just like you), but using a simple array everything seems to be working.