I'm a beginner with LINQ.
How can I convert this to a LINQ statement?
List<Foo> myList = new List<Foo>();
myList.AddRange(// here I add my items);
foreach (Foo x in myList)
{
if (x.IsRequired() == false) throw new Exception();
}
to a LINQ statement? Like:
myList.ForEach(x => //something here);
I tried the following but that didn't work for me.
myList.ForEach(x => if (x.IsRequired() == false) throw new Exception());
I'd say
if (MyList.Any(x => x.IsRequired() == false))
{
throw new Exception();
}
IsRequired() It's a method that returns a Boolean
so you can also shorten
if (MyList.Any(x => !x.IsRequired()))
{
throw new Exception();
}
The answer that fubo gave is good if you just want to see if any of the elements in your list is not required. If you want to get the actual element(s), you can do it like this:
First Element
Foo notRequired = MyList.FirstOrDefault(x => !x.IsRequired());
if ( notRequired != null)
{
// Do something with `notRequired`
}
All Elements
IEnumerable<Foo> notRequired = MyList.Where(x => !x.IsRequired());
if (notRequired.Count() > 0)
{
foreach (var v in notRequired)
{
// Do something with `v`
}
}
After reading your comments and the additional information :
The problem is that I want to find all Foo elements in myList which are not required. It's seems not possible with the Any method, it will fail on the first one.
Assuming Foo has some information that you would like to pass to your exception like a string Information you could get all of them assign them to a new list and check then for Any(). and do all that in the If-Clause:
List<Foo> temp = new List<Foo>();
if ((temp = MyList.Where(x=>!x.IsRequired()).ToList()).Any())
{
// now pass the information of them all into the exception
throw new Exception(String.Join("\t", temp.Select(y=>y.Information)));
}
Officially ForEach is not a LINQ statement. It usually only works for Lists.
From your code I assume that you want to throw an exception if any of the Foo objects in MyList has a false IsRequiredvalue.
You statement would be:
if (MyList.Any(foo => !foo.IsRequired))
throw new Exception();
In words: if any of the foo elements in MyList has a false IsRequired value, throw a new Exception
The nice thing from using Any instead of first creating a list before checking, is that if you have an IEnumerable, and one of the first elements in the list would throw an exception, the rest of your list would not have been created in vain. See StackOverflow: What are the benefits of deferred execution?
Later you wrote:
The problem is that I want to find all Foo elements in myList which
are not required. It's seems not possible with the Any method, it will
fail on the first one.
If you want to find all Foo elements in the list that are not required, you still can use Linq, using Enumerable.Where:
var notRequiredFoos = myList
.Where(elementInList => !elementInList.IsRequired);
usage:
foreach (var notRequiredFoo in notRequiredFoos)
{
Console.WriteLine($"Foo element {notRequiredFoo.ToString} is not required");
}
Or if you want to throw an exception as soon as you found one, Linq will still help you: Enumerable.FirstOrDefault
var notRequiredFoo= myList
.Where(elementInList => !elementInList.IsRequired);
.FirstOrDefault();
if (notRequiredFoo != null)
{ // we found a Foo that is not required
throw new MyException(notRequiredFoo);
}
// else: all Foos are required
Again, you still don't have to check all elements in the list, it will stop as soon as one is found.
Related
I have a list of transactions and i need to find if there is more then 1 account
i did
var MultipleAccounts = list.GroupBy(t => t.AccountId).Count() > 1;
is there a better way?
If you're willing to lose the single-line I prefer the use of !.All(item => bool) or .Any(item => bool) as I think it's the most semantic and easiest to read, as well as being a good candidate for the fastest.
var accountId = accounts[0].AccountId;
var hasMultipleAccounts = !accounts.All(account => account.AccountId == accountId);
Alternatively, and perhaps even more semantically, you could use .Any(item => bool) instead of .All(item => bool).
var accountId = accounts[0].AccountId;
var hasMultipleAccounts = accounts.Any(account => account.AccountId != accountId);
Things to watch out for are making sure you have at least one item (so that accounts[0] doesn't fail) and not doing a multiple enumeration of your IEnumerable. You say you're working with a List, so multiple enumeration shouldn't cause you any trouble, but when you just have an unknown IEnumerable it's important to be careful.
I prefer:
var MultipleAccounts = list.Select(t => t.AccountId).Distinct().Skip(1).Any();
This should be exceedingly fast as it will stop iterating the source list as soon as it finds a second AccountId.
Anytime you execute a full .Count() it has to iterate the full source list.
You can test this with the following code:
void Main()
{
Console.WriteLine(Data().Select(t => t).Distinct().Skip(1).Any());
}
private Random __random = new Random();
public IEnumerable<int> Data()
{
while (true)
{
var #return = __random.Next(0, 10);
Console.WriteLine(#return);
yield return #return;
}
}
A typical run looks like this:
7
9
True
Ok here is what i found the quickest
public bool HasMultipleAccounts(List<Account> list)
{
foreach (var account in list)
if (account.AccountId != list[0].AccountId)
return true;
return false;
}
usage: var MultipleAccounts = HasMultipleAccounts(list);
Credits: #hvd
i know its more code but if you think what the cpu needs to do its the quickest
I have a static set of categories, and an incoming list of items that are in various categories. I want to get the first item that matches the best category, and if none is found, get the first item that matches the next-best category, etc. until I get to a default category.
I tried putting my categories in an IEnumerable and doing a Contains() on it to see if my incoming items match a category, and stopping on the first match. But I can't control the match order: if the category list is ordered by priority [best, OK, default], the first input item to match anything in the category list wins. So if my first input item matches OK, and the second input item matches Best, then I'll stop before I get the Best match.
Right now I run Where() over the item list, and if the result is null I run a second Where(), etc. I'd like to know if there's a more concise (or more LINQ-idiomatic) way to write this:
public MyVM getVM( IEnumerable<Entities.Foo> foos )
{
Entities.Foo foo = null;
MyVM myVM = null;
if ( entity.IsBar )
{
foo = foos.Where( f => f.FooCatId == FooCategories.BestCat ).FirstOrDefault();
}
// no foos are BestCat, look for OkCat
if ( foo == null )
{
foo = foos.Where( f => f.FooCatId == FooCategories.OkCat ).FirstOrDefault();
}
// no foos are OkCat, look for DefaultCat
if ( foo == null )
{
foo = foos.Where( f => f.FooCatId == FooCategories.DefaultCat ).FirstOrDefault();
}
if ( foo != null )
{
myVM = new MyVM() { Name = foo.Name };
}
return myVM;
}
public enum FooCategories
{
DefaultCat,
SomeCat,
AnotherCat,
OkCat,
BestCat,
BadCat
}
There's certainly a more concise way of doing it, in two ways:
Use the overload of FirstOrDefault which takes a predicate
Use the null-coalescing operator
I'm going to ignore your IsBar check for now, because I don't understand how that fits in... but the rest would be:
var foo = foos.FirstOrDefault(f => f.FooCatId == FooCategories.BestCat)
?? foos.FirstOrDefault(f => f.FooCatId == FooCategories.OkCat)
?? foos.FirstOrDefault(f => f.FooCatId == FooCategories.DefaultCat);
Another option would be to change your enum order so that you could just find the cat with the best category - either by using OrderByDescending(f => f.FooCatId) or by using MaxBy from MoreLINQ. You'd also then need to check that the resulting cat isn't a bad cat, etc, so it might not be much of a win - but MaxBy would at least be more efficient, by only going through the list once.
I'm trying to find a neat way to find all of the values in an observable collection which meet a certain criteria. For this example to keep things simple lets say its the collection contains ints and I'm trying to find all of the items that are greater than 5.
The best way I currently know of doing it is like this
ObservableCollection<Int> findAllGreaterThanFive (ObservableCollection<Int> numbers)
{
ObservableCollection<Int> numbersGreaterThanFive;
foreach(Int number in numbers)
{
if (number > 5)
{
numbersGreaterThanFive.add(number);
}
}
return numbersGreaterThanFive;
}
Obviously ignore any simple solutions that take advantage to the fact I'm looking for ints I need a solution that works with any an ObservableCollection of any type with any condition. I was just wondering if checking every item with the foreach loop and the conditional is the best way of doing it?
You can say something like:
var numbersGreaterThanFive = numbers.Where(x => x > 5);
you can use System.Linq namespace, add using statement using System.Linq and after that you can use following Where method.
ObservableCollection<int> list = new ObservableCollection<int>();
list.Where(i => i > 5).ToList();
you can use any kind of objects like :
ObservableCollection<DataItem> list = new ObservableCollection<DataItem>();
list.Where(i => i.ID > 10);
The code above returns DataItem's with ID greater than 10.
If you sure about there's only one record satisfying condition, you can use First() method like :
ObservableCollection<DataItem> list = new ObservableCollection<DataItem>();
list.First(i => i.ID == 10);
Above code returns the DataItem with ID 10. But if there's no record with ID = 10 then it will throw an exception. Avoid of this if you're not sure there's only one record satisfies the condition. Also you can use FirstOrDefault() method.
ObservableCollection<DataItem> list = new ObservableCollection<DataItem>();
DataItem item = list.FirstOrDefault(i => i.ID == 10);
if(item != null)
{
//DoWork
}
If there's no record with ID = 10, then item will be null.
I have a list List<string> with some paths.
C:\Dir\Test\
C:\MyDir\
C:\YourDir\
C:\Dir\
I want to go through all the elements (using LINQ) and remove entries that are started with other element from my list.
In my example C:\Dir\Test\ starts with C:\Dir\ - so I want to remove C:\Dir\Test\.
Use List<T>.RemoveAll() method:
sourceList.RemoveAll(x => sourceList.Any(y => x != y && x.StartsWith(y)));
Try this:
myInitialList.RemoveAll(x =>myInitialList.Any(q => q != x && q.StartsWith(x)));
Or if you want to keep the original list, this is a way to get all the records that do not match your criteria:
List<string> resultList = myInitialList.Except(x => myInitialList.Any(q => q != x && q.StartsWith(x)));
How about
mylist = mylist.Where(a => mylist.All(b => b == a || !a.StartsWith(b)))
.Distinct()
.ToList();
This will return a new list where there isn't another item in the list that it starts with.
It has the extra check to allow returning the value where there string is the same, otherwise all items would be removed from the list.
Finally the distinct call means that two occurrences of the same string are removed.
Building on nsinreal's comment and solution you could do something like
myList = myList.OrderBy(d => d)
.Aggregate(new List<string>(),
(list, item) => {
if (!list.Any(x => item.StartsWith(x)))
list.Add(item);
return list;
}).ToList();
This reduces the complexity of the solution by reducing the size of the search list for each test. It still requires an initial sort.
Personally I find this alternative solution harder to read and my first answer is more expressive the problem to solve.
The most efficient way is IMO to sort the paths, then iterate them and return only the ones not starting as one of the previous, i.e. :
public static IEnumerable<string>
GetRootPathsOfSet(this IEnumerable<string> paths)
{
var sortedSet = new SortedSet<string>(paths,
StringComparer.CurrentCultureIgnoreCase);
string currRoot = null;
foreach (var p in sortedSet)
{
if (currRoot == null ||
!p.StartsWith(currRoot, StringComparison.InvariantCultureIgnoreCase))
{
currRoot = p;
yield return currRoot;
}
}
}
Some notes:
All the paths MUST terminate with a trailing back-slash, otherwise the StartsWith approach is not safe (e.g. C:\Dir and C:\Directory)
This code uses case-insensitive comparison
I'm not using pure LINQ here, but it's an extension method
I am having some trouble in converting the following code to use LINQ.
int occurs = 0;
foreach (string j in items)
{
if (!string.IsNullOrEmpty(j))
{
WorkflowModule tempWM = new WorkflowModule(j);
if (tempWM.StateID == item.StateID)
{
occurs++;
}
}
}
return occurs;
So far, I have:-
var lstItems = (from lstItem in items
where !string.IsNullOrEmpty(lstItem)
let objWorkflowModule = new WorkflowModule(lstItem)
select new
{
tempWM = objWorkflowModule.StateID
}).Where(item.StateID == tempWM));
return lstItems.Count();
but intellisense is not liking the line '.Where(item.StateID == tempWM))'
Can anyone help me achieve this?
Thanks.
When you use the method syntax, you need to use a lambda on the Where operator:
...
}).Where(x => x.tempWM == item.StateID));
In other words, you need to "declare" the variable x which holds the result of the previous part of the query.
It doesn't look like item is initialized anywhere in your statement.
Here's how I'd do this
var lstItems = from lstItem in items
where !string.IsNullOrEmpty(lstItem)
let objWorkflowModule = new WorkflowModule(lstItem)
select objWorkflowModule.StateID;
return lstItems.Count(t=> t == item.StateID);
I'm assuming item is a variable defined outside of the original code you submitted. Basically you don't need to create the anonymous class in the query and you can put the predicate in you're Where into Count instead. But as others have said the main issue is that you need to express your predicate as a lambda.