I'm kinda new to the reactive extensions, but since I have a very data-flow heavy problem, I'm assuming, it could massively simplify my implementation. But it seems my problem is a bit more exotic than I anticipated.
Problem
I have multiple data sources, which all emit part of the data for the same entity. eg I have datasource1, which emits the first name of a person, and datasource2 which emits the last name of a person. The arrival of these data is completely unpredictable.
What I need to do now, is to observe both those sources, and to use some kind of operator or subject, which allows me to await both source-observables. I only want to continue if both datasources return their specific part. Both my sources also pass a key for the data, so it's possible to link the together at a later point.
Is there a construct built into reactive, which allows me to that? Or is reactive simply the wrong toolset to solve my problem?
I can't judge whether Rx or async/await or TPL-Dataflow is a better solution, since that would probably depend on your larger application. Some reproducible code would really help.
Anyhow, here's an Rx solution. I'm assuming for now datasource1 and datasource2 are observables of different types, or easily convertible to observables of different types. If they were observables of the same type, this solution would also work, but you would have other options as well:
var firstNameSource = new Subject<FirstNameMessage>();
var lastNameSource = new Subject<LastNameMessage>();
var timeout = TimeSpan.FromSeconds(1); //Set to length of time willing to wait
var join = firstNameSource.Join(lastNameSource,
fnm => Observable.Timer(timeout),
lnm => Observable.Timer(timeout),
(fnm, lnm) => new { FirstNameMessage = fnm, LastNameMessage = lnm }
)
.Where(a => a.FirstNameMessage.Id == a.LastNameMessage.Id)
.Select(a => Tuple.Create(a.FirstNameMessage.Name, a.LastNameMessage.Name))
.Timeout(timeout)
.Catch(Observable.Empty<Tuple<string, string>>());
Using these sample classes:
public class FirstNameMessage
{
public int Id { get; set; }
public string Name { get; set; }
}
public class LastNameMessage
{
public int Id { get; set; }
public string Name { get; set; }
}
Here's some sample subscription/execution code:
join.Subscribe(t => Console.WriteLine($"{t.Item1} {t.Item2}"), () => Console.WriteLine("No more names!"));
firstNameSource.OnNext(new FirstNameMessage{Id = 1, Name = "John" });
lastNameSource.OnNext(new LastNameMessage{Id = 1, Name = "Smith" });
lastNameSource.OnNext(new LastNameMessage { Id = 2, Name = "Jones" });
await Task.Delay(TimeSpan.FromMilliseconds(500));
firstNameSource.OnNext(new FirstNameMessage { Id = 2, Name = "Paul" });
firstNameSource.OnNext(new FirstNameMessage { Id = 3, Name = "Larry" });
await Task.Delay(TimeSpan.FromMilliseconds(1500));
lastNameSource.OnNext(new LastNameMessage { Id = 3, Name = "Fail" });
firstNameSource.OnNext(new FirstNameMessage { Id = 4, Name = "Won't Work" });
lastNameSource.OnNext(new LastNameMessage { Id = 4, Name = "Subscription terminated" });
Explanation:
The crucial part of this solution is the Join operator. Whereas a standard DB/LINQ Join joins things by key, Rx's Join joins by time window. So the Join above joins any FirstNameMessage and LastNameMessage that are within timeout timespan of each other. Since we also want to join by key, that's why the Where clause is there.
The TimeOut and Catch calls at the end are possibly superfluous: They just serve to terminate the subscription. It sounds like your solution may just be waiting for one value, not multiple, so that may be required.
Related
I have a list as follows which will contain the following poco class.
public class BoxReportView
{
public DateTime ProductionPlanWeekStarting { get; set; }
public DateTime ProductionPlanWeekEnding { get; set; }
public string BatchNumber { get; set; }
public string BoxRef { get; set; }
public string BoxName { get; set; }
public decimal Qty { get; set; }
public FUEL_KitItem KitItem { get; set; }
public decimal Multiplier { get; set; }
}
I am wanting to group the report and sum it by using the BoxName and also the Qty SO I tried the following
var results = from line in kitItemsToGroup
group line by line.BoxName into g
select new BoxReportView
{
BoxRef = g.First().BoxRef,
BoxName = g.First().BoxName,
Qty = g.Count()
};
In My old report I was just doing this
var multiplier = finishedItem.SOPOrderReturnLine.LineQuantity -
finishedItem.SOPOrderReturnLine.StockUnitDespatchReceiptQuantity;
foreach (KitItem kItem in kitItems.Cast<KitItem().Where(z => z.IsBox == true).ToList())
{
kittItemsToGroup.Add(new BoxReportView() {
BatchNumber = _batchNumber,
ProductionPlanWeekEnding = _weekEndDate,
ProductionPlanWeekStarting = _weekStartDate,
BoxRef = kItem.StockCode,
KitItem = kItem,
Multiplier = multiplier,
Qty = kItem.Qty });
}
}
Then I was just returning
return kitItemsToGroup;
But as I am using it as a var I cannot what is best way to handle the grouping and the sum by box name and qty.
Whether it is the best way depends upon your priorities. Is processing speed important, or is it more important that the code is easy to understand, easy to test, easy to change and easy to debug?
One of the advantages of LINQ is, that it tries to avoid enumeration of the source more than necessary.
Are you sure that the users of this code will always need the complete collection? Can it be, that now, or in near future, someone only wants the first element? Or decides to stop enumeration after he fetched the 20th element and saw that there was nothing of interest for him?
When using LINQ, try to return IEnumerable<...> as long as possible. Let only the end-user who will interpret your LINQed data decide whether he wants to take only the FirstOrDefault(), or Count() everything, or put it in a Dictionary, or whatever. It is a waste of processing power to create a List if it is not going to be used as a List.
your LINQ code and your foreach do some completely different things. Alas it is quite common here on StackOverflow for people to ask for LINQ statements without really specifying their requirements. So I'll have to guess something in between your LINQ statement and your foreach.
Requirement Group the input sequence of kitItems, which are expected to be Fuel_KitItems into groups of BoxReportViews with the same BoxName, and select several properties from every Fuel_KitItem in each group.
var kitItemGroups = kitItems
.Cast<Fuel_KitItem>() // only needed if kitItems is not IEnumerable<Fuel_KitItem>
// make groups of Fuel_KitItems with same BoxName:
.GroupBy(fuelKitItem => fuelKitItem.BoxName,
// ResultSelector, take the BoxName and all fuelKitItems with this BoxName:
(boxName, fuelKitItemsWithThisBoxName) => new
{
// Select only the properties you plan to use:
BoxName = boxName,
FuelKitItems = fuelKitItemsWithThisBoxName.Select(fuelKitItem => new
{
// Only Select the properties that you plan to use
BatchNumber = fuelKitItem.BatchNumber,
Qty = fuelKitItem.Qty,
...
// Not needed, they are all equal to boxName:
// BoxName = fuelKitItem.BoxName
})
// only do ToList if you are certain that the user of the result
// will need the complete list of fuelKitItems in this group
.ToList(),
});
Usage:
var kitItemGroups = ...
// I only need the KitItemGroups with a BoxName starting with "A"
var result1 = kitItemGroups.Where(group => group.BoxName.StartsWith("A"))
.ToList();
// Or I only want the first three after sorting by group size
var result2 = kitItemGroups.OrderBy(group => group.FuelKitItems.Count())
.Take(3)
.ToList();
Efficiency Improvements: As long as you don't know how your LINQ will be used, don't make it a List. If you know that chances are high that the Count of group.FuelKitItems is needed, to a ToList
I'm reading C# In Depths to try and better understand the language. I've used simple lambda expressions before with a single parameter and have become familiar with them. The part I'm struggling with is films.Sort((f1, f2) => f1.Name.CompareTo(f2.Name)); to sort the list. From what I've been able to figure out the lambda expression evaluates to IComparer<Film> when I tried to add f3 to it. The method being called IComparer.Compare Method (T, T) determines the items order.
The second parameter makes me want to say that it's comparing the Nth and Nth+1 film in the list and doing that from 0 through films.Count-1. Is this correct? If not, what part am I mistaken on. I wan't to avoid assuming incorrectly and avoid unintended errors.
using System;
using System.Collections.Generic;
public class Program
{
public static void Main()
{
var films = GetFilms();
Action<Film> print = film => Console.WriteLine("Name={0}, Year={1}", film.Name, film.Year);
Console.WriteLine("All films");
films.ForEach(print);
Console.WriteLine();
Console.WriteLine("Old films");
films.FindAll(film => film.Year < 1960).ForEach(print);
Console.WriteLine();
Console.WriteLine("Sorted films");
films.Sort((f1, f2) => f1.Name.CompareTo(f2.Name));
films.ForEach(print);
}
class Film
{
public string Name { get; set; }
public int Year { get; set; }
}
static List<Film> GetFilms()
{
return new List<Film>
{
new Film { Name = "Jaws", Year = 1975 },
new Film { Name = "Singing in the Rain", Year = 1952 },
new Film { Name = "Some like it Hot", Year = 1959 },
new Film { Name = "The Wizard of Oz", Year = 1939 },
new Film { Name = "It's a Wonderful Life", Year = 1946 },
new Film { Name = "American Beauty", Year = 1999 },
new Film { Name = "High Fidelity", Year = 2000 },
new Film { Name = "The Usual Suspects", Year = 1995 }
};
}
}
You can't tell from the method signature how many times the argument will be used. I could write a method Foo(Func<string, string>) that never called its argument.
However, since this is a sorting method, it's not enough to iterate once over the list. There are lots of different sorting algorithms, but they tend to use O(n log(n)) comparisons. In other words, doubling the length of the list sorted will result in slightly more than double the calls to your lambda function.
If you want to see what actually happens when it's running, add some logging!
films.Sort((f1, f2) =>
{
Console.WriteLine("Comparing ${f1.Name} to ${f2.Name}");
return f1.Name.CompareTo(f2.Name);
});
Actually you can use LINQ for sorting elements on any type that implements IEnumerable<T> interface like List<T> type:
// This will order the films by their name.
var result1 =
films
.OrderBy(film => film.Name)
.ToList();
// This will order the films first by Year in descending order and
// then by Name in ascending order.
var result2 =
films
.OrderByDescending(film => film.Year)
.ThenBy(film => film.Name)
.ToList();
There is also a ThenByDescending() method you can use and also you can create a longer chain from these methods if needed.
The thing is that here you should select only one property at a time in the lambda expression.
Sorry for the incoherent title. I don't know how to concisely explain my problem, which is why I didn't really know how to look it up. I'll explain using an example...
Let's say I have a class:
public class cas
{
public string name { get; set; }
public int num { get; set; }
}
With that class, I make several objects and stick them into a list. For the sake of example, I will make 4:
var list = new List<cas>
{
new cas { name = "firstname", num = 1 },
new cas { name = "firstname", num = 2 },
new cas { name = "lastname", num = 3 },
new cas { name = "lastname", num = 4 }
};
Is there a way to take this List and combine any objects with the same name field?
So, the new list would be 1 object with:
name = "firstname", num = 3,
name = "lastname", num = 7
There's the obvious "long" way to do it, but it would be clunky and expensive (go through the list several times to find like-objects). I was wondering if I was missing any clean way of doing it. I intentionally made a simple example so that the answer would be a proof of concept rather than writing my code for me. My actual problem is more complex than this, but I can't figure out this one aspect of it.
Using Linq, you have a GroupBy Method and a Select Method:
list = list.GroupBy(x=> x.name)
.Select(x=> new cas() { name = x.Key, num = x.Sum(y=> y.num) }).ToList();
Or using Elegant query-syntax:
list = (from item in list
group item by item.name into grouping
select new cas()
{
name = grouping.Key,
num = grouping.Sum(x => x.num)
}).ToList();
Note that to use these methods, you have to add using System.Linq at the top of your source file.
You can use linq, you would have to group them on name property and then sum on the num property of each group like:
var result = list.GroupBy(x=>x.name)
.Select(g=> new cas
{
name = g.Key,
num = g.Sum(x=>x.num)
});
I need to update all the properties of a given node, using mutating cypher. I want to move away from Node and NodeReference because I understand they are deprecated, so can't use IGraphClient.Update. I'm very new to mutating cypher. I'm writing in C#, using Neo4jclient as the interface to Neo4j.
I did the following code which updates the "Name" property of a "resunit" where property "UniqueId" equals 2. This works fine. However,
* my resunit object has many properties
* I don't know which properties have changed
* I'm trying to write code that will work with different types of objects (with different properties)
It was possible with IGraphClient.Update to pass in an entire object and it would take care of creating cypher that sets all properies.
Can I somehow pass in my object with mutating cypher as well?
The only alternative I can see is to reflect over the object to find all properties and generate .Set for each, which I'd like to avoid. Please tell me if I'm on the wrong track here.
string newName = "A welcoming home";
var query2 = agencyDataAccessor
.GetAgencyByKey(requestingUser.AgencyKey)
.Match("(agency)-[:HAS_RESUNIT_NODE]->(categoryResUnitNode)-[:THE_UNIT_NODE]->(resunit)")
.Where("resunit.UniqueId = {uniqueId}")
.WithParams(new { uniqueId = 2 })
.With("resunit")
.Set("resunit.Name = {residentialUnitName}")
.WithParams(new { residentialUnitName = newName });
query2.ExecuteWithoutResults();
It is indeed possible to pass an entire object! Below I have an object called Thing defined as such:
public class Thing
{
public int Id { get; set; }
public string Value { get; set; }
public DateTimeOffset Date { get; set; }
public int AnInt { get; set; }
}
Then the following code creates a new Thing and inserts it into the DB, then get's it back and updates it just by using one Set command:
Thing thing = new Thing{AnInt = 12, Date = new DateTimeOffset(DateTime.Now), Value = "Foo", Id = 1};
gc.Cypher
.Create("(n:Test {thingParam})")
.WithParam("thingParam", thing)
.ExecuteWithoutResults();
var thingRes = gc.Cypher.Match("(n:Test)").Where((Thing n) => n.Id == 1).Return(n => n.As<Thing>()).Results.Single();
Console.WriteLine("Found: {0},{1},{2},{3}", thingRes.Id, thingRes.Value, thingRes.AnInt, thingRes.Date);
thingRes.AnInt += 100;
thingRes.Value = "Bar";
thingRes.Date = thingRes.Date.AddMonths(1);
gc.Cypher
.Match("(n:Test)")
.Where((Thing n) => n.Id == 1)
.Set("n = {thingParam}")
.WithParam("thingParam", thingRes)
.ExecuteWithoutResults();
var thingRes2 = gc.Cypher.Match("(n:Test)").Where((Thing n) => n.Id == 1).Return(n => n.As<Thing>()).Results.Single();
Console.WriteLine("Found: {0},{1},{2},{3}", thingRes2.Id, thingRes2.Value, thingRes2.AnInt, thingRes2.Date);
Which gives:
Found: 1,Foo,12,2014-03-27 15:37:49 +00:00
Found: 1,Bar,112,2014-04-27 15:37:49 +00:00
All properties nicely updated!
I have a list like
List<VoieData> listVoieData = new List<VoieData>();
and in VoieData Class I have :
public class VoieData
{
public int Depart { set; get; }
public int Arrive { set; get; }
public int DistanceDepart { set; get; }
public int DistanceArrive { set; get; }
}
Since I have a massive values I want to only consider all my Depart number , I would like to filter the listVoieData by finding the Arrive only have the same value as the
Depart
for example I have
listVoieData.Select(p=>p.Depart).ToList()= List<int>{1,2,3};
listVoieData.Select(p=>p.Arrive).ToList()= List<int>{1,2,3,4,5};
I need to throw away the entire VoieData which contain {4,5} as Arrive
right now my soulution is like this , but it' s not correct ;
List<VoieData> listVoieDataFilter = listVoieData .Join(listVoieData , o1 => o1.Arrive, o2 => o2.Depart, (o1, o2) => o1).ToList();
Sorry for the confusing question ;
I want to remove Arrive which is different from all the Depart in the list list , and return the new
List
it 's not only in one VoieData;
Arrive!=Depart
Thanks
I think you want to remove all objects where Arrive is not in any of the Depart from any object. In that case, first get all Depart and then filter by Arrive:
HashSet<int> allDepart = new HashSet<int>(listVoieData.Select(x => x.Depart));
var result = listVoieData.Where(v => !allDepart.Contains(v.Arrive))
We use a HashSet<int> for efficiency.
Use LINQ Where:
var records = listVoieData.Where(x => x.Arrive == x.Depart);
This will return results where both Arrive and Depart are the same.
That would be a typical case to use linq.
something like:
var res = from data in listVoieData
where data.Depart == data.Arrive
select data;
and then optionally just use res.ToArray() to run the query and get the array.
Since you've stated that you want:
I want to remove Arrive which is different from all the Depart
This can be re-phrased as, "The set of all arrivals except those in the set of departures", which translates very nicely into the following LINQ query:
var arrivalsWithNoDepartures = listVoieData.Select(p=>p.Arrive)
.Except(listVoieData.Select(p=>p.Depart));