Anyone knows of a more concise/elegant way of achieving the following?
A = B if B?
Thanks.
EDIT:
I'm looking for a solution that references A and B once only. And would compile to
if (typeof B !== "undefined" && B !== null) { A = B; }
or something else similar.
To have this short helps have the following a bit more readable:
someObject[someAttribute] = (someOtherObject[someOtherAttribute] if someOtherObject[someOtherAttribute]?)
That is the motivation for my question.
You could say:
a = b ? a
For example, this:
a = 11
a = b ? a
console.log(a)
b = 23
a = b ? a
console.log(a)
will give you 11 and 23 in the console (demo: http://jsfiddle.net/ambiguous/ngtEE/)
Maybe something like:
A=_ if (_=B)?
expanded:
if ((_ = B) != null) {
A = _;
}
This will overwrite A with what ever is in B, but only if it is not null, referencing both only once.
Not sure about Coffee Script but you can use the OR operator for this in regular javascript like so:
a = b || a
Related
I have a special class Model that needs to have its methods called in a very specific order.
I tried doing something like this:
val model = new Model
new MyWrappingClass {
val first = model.firstMethod()
val second = model.secondMethod()
val third = model.thirdMethod()
}
The methods should be called in the order listed, however I am seeing an apparently random order.
Is there any way to get the variable initialization methods to be called in a particular order?
I doubt your methods are called in the wrong order. But to be sure, you can try something like this:
val (first, second, third) = (
model.firstMethod(),
model.secondMethod(),
model.thirdMethod()
)
You likely have some other problem with your code.
I can run 100 million loops where it never gets the order wrong, as follows:
class Model {
var done = Array(false,false,false);
def firstMethod():Boolean = { done(0) = true; done(1) || done(2) };
def secondMethod():Boolean = { done(1) = true; !done(0) || done(2) };
def thirdMethod():Boolean = { done(2) = true; !done(0) || !done(1) };
};
Notice that these methods return a True if done out of order and false when called in order.
Here's your class:
class MyWrappingClass {
val model = new Model;
val first = model.firstMethod()
val second = model.secondMethod()
val third = model.thirdMethod()
};
Our function to check for bad behavior on each trial:
def isNaughty(w: MyWrappingClass):Boolean = { w.first || w.second || w.third };
A short program to test:
var i = 0
var b = false;
while( (i<100000000) && !b ){
b = isNaughty(new MyWrappingClass);
i += 1;
}
if (b){
println("out-of-order behavior occurred");
println(i);
} else {
println("looks good");
}
Scala 2.11.7 on OpenJDK8 / Ubuntu 15.04
Of course this doesn't prove it impossible to have wrong order, only that correct behavior seems highly repeatable in a fairly simple case.
I have two value streams and one selector stream and I'd like to produce a result stream that alternates between the value streams based on the selector. The code below gives the right result, but I don't like it.
Does anyone have anything neater?
var valueStreamA = new BehaviorSubject<int>(0);
var valueStreamB = new BehaviorSubject<int>(100);
var selectorStream = new BehaviorSubject<bool>(true);
var filteredA = valueStreamA .CombineLatest(selectorStream, (a, c) => new { A = a, C = c })
.Where(ac => ac.C)
.Select(ac => ac.A);
var filteredB = valueStreamB.CombineLatest(selectorStream, (b, c) => new { B = b, C = c })
.Where(bc => !bc.C)
.Select(bc => bc.B);
var result = Observable.Merge(filteredA, filteredB);
result.Subscribe(Console.WriteLine);
valueStreamA.OnNext(1);
valueStreamB.OnNext(101);
selectorStream.OnNext(false);
valueStreamA.OnNext(2);
valueStreamB.OnNext(102);
selectorStream.OnNext(true);
This productes the following output:
0
1
101
102
2
I'd do something like this:
var a = new BehaviorSubject<int>(0);
var b = new BehaviorSubject<int>(100);
var c = new BehaviorSubject<bool>(true);
var valueStreamA = a as IObservable<int>;
var valueStreamB = b as IObservable<int>;
var selector = c as IObservable<bool>;
var result = selector
// for every change in the selector...
.DistinctUntilChanged()
// select one of the two value streams
.Select(change => change ? valueStreamA : valueStreamB)
// and flatten the resulting wrapped observable
.Switch();
result.Subscribe(Console.WriteLine);
a.OnNext(1);
b.OnNext(101);
c.OnNext(false);
a.OnNext(2);
b.OnNext(102);
c.OnNext(true);
Could do something like:
var xs = Observable.Interval(TimeSpan.FromSeconds(1)).Select(_ => Feeds.Xs);
var ys = Observable.Interval(TimeSpan.FromSeconds(1)).Select(_ => Feeds.Ys);
var selectorSubject = new Subject<Feeds>();
var query = from selector in selectorSubject
select from merged in xs.Merge(ys)
where merged == selector
select merged;
query.Switch().Subscribe(Console.WriteLine);
OnNext into your 'selectorSubject' to change it.
There are a few differences to your example, but easy to get around:
Your question involved a selector of type bool, whereas I have been lazy and reused the Feeds enum in order to allow me to do an easy equality check (where merged == selector).
You of course could simply do (where selector ? merged == Xs : merged == Ys), or something like that to evaluate each merged item and discard ones you don't care about (depending on your selector).
Specifically, you would probably want to select not just the integer, but an identifier of the feed. Consider using something like Tuple.Create(), so you get that info with each update:
{A - 1}, {B - 101} etc. Your where can then do:
where selector ? merged.Item1 == A : merged.Item1 == B //this maps 'true' to feed A
I also used a Switch, which will cause my sample streams to restart because they are not published.
You probably want to publish yours and Connect them (make them 'hot'), so a Switch like mine doesn't cause any new side effects in the subscription. You have a subject (which is hot), but the 'behaviour' part will replace the value you passed into the constructor. Publishing and connecting would prevent that.
Shout if you are still confused. This isn't a full answer, but might give you enough to think about.
Howard.
Now much closer to your original question:
void Main()
{
var valueStreamA = new BehaviorSubject<int>(0);
var valueStreamB = new BehaviorSubject<int>(100);
var selectorStreamA = valueStreamA.Select(id => Tuple.Create("A", id)).Publish();
var selectorStreamB = valueStreamB.Select(id => Tuple.Create("B", id)).Publish();
var selectorStream = new BehaviorSubject<bool>(true);
var query = from selector in selectorStream
select from merged in selectorStreamA.Merge(selectorStreamB)
where selector == true ? merged.Item1 == "A" : merged.Item1 == "B"
select merged.Item2;
query.Switch().Subscribe(Console.WriteLine);
selectorStreamA.Connect();
selectorStreamB.Connect();
//First we get 0 output (because we are already using stream A, and it has a first value)
valueStreamA.OnNext(1); //This is output, because our selector remains as 'A'
valueStreamB.OnNext(101); //This is ignored - because we don't take from B
selectorStream.OnNext(false); //Switch to B
valueStreamA.OnNext(2); //Ignored - we are now using B only
valueStreamB.OnNext(102); //This is output
selectorStream.OnNext(true); //Switch back to A.
}
Outputs:
0
1
102
Let's say we have a description field on my form with optional check boxes. The check boxes represent which fields to search when doing the lookup. Right now I have a matrix of look ups that call their unique version of where clause. It works but I think it smells a bit.
Here is an excerpt
// Look for part numbers decide how many fields to search and use that one.
// 0 0 X
if (!PartOpt[0] && !PartOpt[1] && PartOpt[2])
{
query = query.Where(p => (p.PartNumAlt2.Contains(partSearchRec.inventory.PartNum)));
}
// 0 X 0
if (!PartOpt[0] && PartOpt[1] && !PartOpt[2])
{
query = query.Where(p => (p.PartNumAlt.Contains(partSearchRec.inventory.PartNum)));
}
// 0 X X
if (!PartOpt[0] && PartOpt[1] && PartOpt[2])
{
query = query.Where(p => (p.PartNumAlt.Contains(partSearchRec.inventory.PartNum)
|| p.PartNumAlt2.Contains(partSearchRec.inventory.PartNum)));
}
// X 0 0
if (PartOpt[0] && !PartOpt[1] && !PartOpt[2])
{
query = query.Where(p => (p.PartNum.Contains(partSearchRec.inventory.PartNum)));
}
. . .
This goes on for a while and seems to be prone to coding errors. In each case we are looking for the same information in any of the selected fields. If I was doing this in SQL I could simply build up the WHERE clause as needed.
Once again I rubber ducked my way to an answer. Rather than throw the question away, here is what I came up with. Is it efficient?
if (partSearchRec.optPartNum || partSearchRec.optAltPartNum1 || partSearchRec.optAltPartNum2)
{
query = query.Where(p => (
(partSearchRec.optPartNum && p.PartNum.Contains(partSearchRec.inventory.PartNum))
|| (partSearchRec.optAltPartNum1 && p.PartNumAlt.Contains(partSearchRec.inventory.PartNum))
|| (partSearchRec.optAltPartNum2 && p.PartNumAlt2.Contains(partSearchRec.inventory.PartNum))));
}
Basically if any of the check boxes are set we will execute the query. Each line of the query will be processed only if the check box was checked. If the left side of an AND is false it doesn't process the right.
This is an aera that Delphi's with statement would be handy. I also learned that you can't use an array inside the LINQ statement.
I have the folowwing statement and I would like to have a LINQ equivalent:
SELECT *
FROM People
where Name like '%something%'
ORDER BY CASE
WHEN Name LIKE 'something%' then 1
WHEN Name LIKE '%something%' then 2
ELSE 3 END
Basically, I'm retrieving all the rows which contains a value (in this case 'something') and I'm ordering them: first the ones starting with that value, and then the remaining.
Any idea on how to do that in LinQ?
I've came out with the following solution.
var dc = new EntityContext();
var result = dc
// Condition part
.People.Where(x => x.Name.IndexOf("Foo") > -1) // This part is translated to like
// projection part
.Select(x => new { Person = x, Weight = x.Name.IndexOf("Bar") > -1 ? 1 : (x.Name.IndexOf("Baz") ? 2 : 0)})
// Order
.OrderBy(x => x.Weight)
// Final projection
.Select(x => x.Person);
I guess everything is self explanatory. First you select under your condition, then create a new object with weights necessary, then order it and finally take the necessary people.
I am not able to verify this, but something like this might work. The code can definitely be optimized/cleaned up, but in theory this just might work :)
The only question is whether the contains in the comparable delegate will translate the way it does in the Where. So, you might need to use an IndexOf or similar (as Oybek implemented)
var queryResult =
people
.Where(person=>person.name.Contains(#"/something/"))
.OrderBy(person=>person.Name,
delegate(string name1, string name2)
{
int result1, result2;
if(name1.Contains(#"something/")) result1 = 1;
else if(name1.Contains(#"/something/")) result1 = 2;
else result1 = 3;
if(name2.Contains(#"something/")) result2 = 1;
else if(name2.Contains(#"/something/")) result2 = 2;
else result2 = 3;
return result1.CompareTo(result2);
})
var svc = new LocationDataServiceContext();
var q = from c in svc.LocationTable
where c.ID == int.Parse(location.ID)
select c;
if (q.ToArray().Length == 0)
id there a neater way to do this?
yes, I believe so...
var svc = new LocationDataServiceContext();
if (svc.LocationTable.SingleOrDefault(c => c.ID == int.Parse(location.ID) != null))
{
}
I thought there was an Exist() method... but I guess not.