I have 3 .net Lists items, I need to merge them all into one, to order them and bind them to a datagrid. However, I need a way of indicating which original list each item came from, so that I can identify this in the datagrid (change color or font etc).
Can anyone suggest the best way to do this?
List<Foo> list1 = new List<Foo>();
List<Foo> list2 = new List<Foo>();
List<Foo> list3 = new List<Foo>();
var query = list1.Select(foo => new { foo, list = "list1" })
.Concat(list2.Select(foo => new { foo, list = "list2" }))
.Concat(list3.Select(foo => new { foo, list = "list3" }))
.OrderBy(item => item.foo); // whatever you need to order by
Expand the properties as needed.
Assuming that your lists contains items of classes that you can amend I'd suggest that you add a property to those classes that keeps track of which type of the 3 it is. Either as an enum or possibly a reference to the actual list that contained it if you might need to refer back.
If you're not able to do that but assuming that they do contain a name property or similar and it's a readonly grid, a very ugly way would be to add a specific prefix/postfix to the name that says where it came from and then just remove that prefix/postfix before showing it on the screen.
Simple solution, assuming you don't want to modify the original class, or it's a primitive, you can use anonymous types:
var resultList = list1.Select(value => new {value, list = list1})
.Concat(list2.Select(value => new {value, list = list2})
.Concat(list3.Select(value => new {value, list = list3})))
.ToList();
I'd go with something like this:
List<object> list1 = new List<object>();
List<object> list2 = new List<object>();
List<object> list3 = new List<object>();
List<KeyValuePair<int, object>> mergedList = new List<KeyValuePair<int, object>>();
mergedList.AddRange(list1.Select(obj => new KeyValuePair<int, object>(1, obj)));
mergedList.AddRange(list2.Select(obj => new KeyValuePair<int, object>(2, obj)));
mergedList.AddRange(list3.Select(obj => new KeyValuePair<int, object>(3, obj)));
The better solution though, would be to add a property to your object that is some kind of enumeration that tells you something about the object itself. The lists themselves are metadata of some sort - list1 is a list of X, not just a list, so all of it's elements should have some kind of notion of X.
Related
say if I had multiple lists created to hold some value. For example:
List<string> ListA= new List<string>();
List<string> ListB= new List<string>();
List<string> ListC= new List<string>();
List<int> ListD= new List<int>();
List<int> ListE= new List<int>();
Are there anyway to clear all list with one-liner? Currently, I'm doing this:
ListA.Clear();
ListB.Clear();
ListC.Clear();
ListD.Clear();
ListE.Clear();
No - not really.
You could create an extension method for this or just move it to a function. Whether that would be better would depend on the situation.
Unless you have nested lists or a or something i would definitely not bother.
You could of course add them all to a collection, and use foreach to call .clear() on each list but again - this depends on the situation.
You could, and without using another collection:
foreach (var list in Enumerable.Range(0, 5).Select<int, IList>(i => i switch { 0 => ListA, 1 => ListB, 2 => ListC, 3 => ListD, 4 => ListE })) list.Clear();
Not that it's any more readable than using 5 lines.
A cleaner solution solution would be to define a helper method:
void Clear(params IList[] lists)
{
foreach (var list in lists) list.Clear();
}
Then:
Clear(ListA, ListB, ListC, ListD, ListE);
I can give you some longer uglier ways...
new List<IList>() { ListA , ListB, ListC, ListD, ListE }.ForEach(x => x.Clear());
and
public static void ClearAll(params IList[] lists)
=> lists.ToList().ForEach(x => x.Clear());
// usage
ClearAll(ListA , ListB, ListC, ListD, ListE);
However, instead of multiple lists, you could just 1 list and a custom class
I have a dictionary which has an integer Key that represents a year, and a Value which is a list of object Channel. I need to flatten the data and create a new object from it.
Currently, my code looks like this:
Dictionary<int, List<Channel>> myDictionary;
foreach(var x in myDictionary)
{
var result = (from a in x.Value
from b in anotherList
where a.ChannelId == b.ChannelId
select new NewObject
{
NewObjectYear = x.Key,
NewObjectName = a.First().ChannelName,
}).ToList();
list.AddRange(result);
}
Notice that I am using the Key to be the value of property NewObjectYear.
I want to get rid of foreach since the dictionary contains a lot of data and doing some joins inside the iteration makes it very slow. So I decided to refactor and came up with this:
var flatten = myDictionary.SelectMany(x => x.Value.Select(y =>
new KeyValuePair<int, Channel>(x.Key, y))).ToList();
But with this, I couldn't get the Key directly. Using something like flatten.Select(x => x.Key) is definitely not the correct way. So I tried finding other ways to flatten that would be favorable for my scenario but failed. I also thought about creating a class which will contain the year and the list from the flattened but I don't know how.
Please help me with this.
Also, is there also another way that doesn't have the need to create a new class?
It seems to me you are trying to do only filtering, you do not need join for that:
var anotherListIDs = new HashSet<int>(anotherList.Select(c => c.ChannelId));
foreach (var x in myDictionary)
{
list.AddRange(x.Value
.Where(c => anotherListIDs.Contains(c.ChannelId))
.Select(c => new NewObject
{
NewObjectYear = x.Key,
NewObjectName = c.First().ChannelName,
}));
}
You do realise, that if the second element of the list in a specific dictionary element has a matching channelId, that you return the first element of this list, don't you?
var otherList = new OtherItem[]
{
new OtherItem() {ChannelId = 1, ...}
}
var dictionary = new Dictionary<int, List<Channel>[]
{
{ 10, // Key
new List<Channel>() // Value
{
new Channel() {ChannelId = 100, Name = "100"},
new Channel() {ChannelId = 1, Name = "1"},
},
};
Although the 2nd element has a matching ChannelId, you return the Name of the first element.
Anyway, let's assume this is what you really want. You are right, your function isn't very efficient.
Your dictionary implements IEnumerable<KeyValuePair<int, List<Channel>>. Therefore every x in your foreach is a KeyValuePair<int, List<Channel>. Every x.Value is a List<Channel>.
So for every element in your dictionary (which is a KeyValuePair<int, List<Channel>), you take the complete list, and perform a full inner join of the complete list with otherList, and for the result you take the key of the KeyValuePair and the first element of the List in the KeyValuePair.
And even though you might not use the complete result, but only the first or the first few, because of FirstOrDefault(), or Take(3), you do this for every element of every list in your Dictionary.
Indeed your query could be much more efficient.
As you use the ChannelIds in your OtherList only to find out if it is present, one of the major improvements would be to convert the ChannelIds of OtherList to a HashSet<int> where you have superior fast lookup to check if the ChannelId of one of the values in your Dictionary is in the HashSet.
So for every element in your dictionary, you only have to check every ChannelId in the list to see if one of them is in the HashSet. As soon as you've found one, you can stop and return only the first element of the List and the Key.
My solution is an extension function of Dictionary>. See Extension Methods Demystified
public static IEnumerable<NewObject> ExtractNewObjects(this Dictionary<int, List<Channel>> dictionary,
IEnumerable<OtherItem> otherList)
{
// I'll only use the ChannelIds of the otherList, so extract them
IEnumerable<int> otherChannelIds = otherList
.Select(otherItem => otherItem.ChannelId);
return dictionary.ExtractNewObjects(otherChannelIds);
}
This calls the other ExtractNewobjects:
public static IEnumerable<NewObject> ExtractNewObjects(this Dictionary<int, List<Channel>> dictionary,
IEnumerable<int> otherChannelIds)
{
var channelIdsSet = new HashSet<int>(otherChannelIds));
// duplicate channelIds will be removed automatically
foreach (KeyValuePair<int, List<Channel>> keyValuePair in dictionary)
{
// is any ChannelId in the list also in otherChannelIdsSet?
// every keyValuePair.Value is a List<Channel>
// every Channel has a ChannelId
// channelId found if any of these ChannelIds in in the HashSet
bool channelIdFound = keyValuePair.Value
.Any(channel => otherChannelIdsSet.Contains(channel.ChannelId);
if (channelIdFound)
{
yield return new NewObject()
{
NewObjectYear = keyValuePair.Key,
NewObjectName = keyValuePair.Value
.Select(channel => channel.ChannelName)
.FirstOrDefault(),
};
}
}
}
usage:
IEnumerable<OtherItem> otherList = ...
Dictionary<int, List<Channel>> dictionary = ...
IEnumerable<Newobject> extractedNewObjects = dictionary.ExtractNewObjects(otherList);
var someNewObjects = extractedNewObjects
.Take(5) // here we see the benefit from the yield return
.ToList();
We can see four efficiency improvements:
the use of HashSet<int> enables a very fast lookup to see if the ChannelId is in OtherList
the use of Any() stops enumerating the List<Channel> as soon as we've found a matching Channelid in the HashSet
the use of yield return makes that you don't enumerate over more elements in your Dictionary than you'll actually use.
The use of Select and FirstOrDefault when creating NewObjectName prevents exceptions if List<Channel> is empty
In my C# code I have a list List<Tuple<int,string>>. I want to select/convert this to a List<Type>. I want to avoid iterating my list of tuple and insert in other list. Is there any way to do this? Maybe with LINQ?
You cannot change type of list. You only can create new list of another type and fill it with converted values from your list. I suggest to use List<T>.ConvertAll method which exists exactly for this purpose:
List<Tuple<int, string>> tuples = new List<Tuple<int, string>>();
// ...
List<YourType> types =
tuples.ConvertAll(t => new YourType { Foo = t.Item1, Bar = t.Item2 });
You haven't shown this type, but i assume that it contains an int- and a string-property:
List<MyType> result = tupleList
.Select(t => new MyType { IntProperty = t.Item1, StringProperty = t.Item2 })
.ToList();
another option: List.ConvertAll:
List<MyType> result = tupleList.ConvertAll(t => new MyType { IntProperty = t.Item1, StringProperty = t.Item2 });
This presumes that your List<Type> is actually a List<CustomType> (I've called it MyType).
I want to avoid iterating my list of tuple and insert in other list.
LINQ does not avoid loops, it hides them just.
I'm trying to figure out how to traverse a generic list of items that I want to remove from another list of items.
So let's say I have this as a hypothetical example
List<car> list1 = GetTheList();
List<car> list2 = GetSomeOtherList();
I want to traverse list1 with a foreach and remove each item in List1 which is also contained in List2.
I'm not quite sure how to go about that as foreach is not index based.
You can use Except:
List<car> list1 = GetTheList();
List<car> list2 = GetSomeOtherList();
List<car> result = list2.Except(list1).ToList();
You probably don't even need those temporary variables:
List<car> result = GetSomeOtherList().Except(GetTheList()).ToList();
Note that Except does not modify either list - it creates a new list with the result.
You don't need an index, as the List<T> class allows you to remove items by value rather than index by using the Remove function.
foreach(car item in list1) list2.Remove(item);
In my case I had two different lists, with a common identifier, kind of like a foreign key.
The second solution cited by "nzrytmn":
var result = list1.Where(p => !list2.Any(x => x.ID == p.ID && x.property1 == p.property1)).ToList();
Was the one that best fit in my situation.
I needed to load a DropDownList without the records that had already been registered.
Thank you !!!
This is my code:
t1 = new T1();
t2 = new T2();
List<T1> list1 = t1.getList();
List<T2> list2 = t2.getList();
ddlT3.DataSource= list2.Where(s => !list1.Any(p => p.Id == s.ID)).ToList();
ddlT3.DataTextField = "AnyThing";
ddlT3.DataValueField = "IdAnyThing";
ddlT3.DataBind();
I would recommend using the LINQ extension methods. You can easily do it with one line of code like so:
list2 = list2.Except(list1).ToList();
This is assuming of course the objects in list1 that you are removing from list2 are the same instance.
list1.RemoveAll(l => list2.Contains(l));
You could use LINQ, but I would go with RemoveAll method. I think that is the one that better expresses your intent.
var integers = new List<int> { 1, 2, 3, 4, 5 };
var remove = new List<int> { 1, 3, 5 };
integers.RemoveAll(i => remove.Contains(i));
Solution 1 : You can do like this :
List<car> result = GetSomeOtherList().Except(GetTheList()).ToList();
But in some cases may this solution not work. if it is not work you can use my second solution .
Solution 2 :
List<car> list1 = GetTheList();
List<car> list2 = GetSomeOtherList();
we pretend that list1 is your main list and list2 is your secondry list and you want to get items of list1 without items of list2.
var result = list1.Where(p => !list2.Any(x => x.ID == p.ID && x.property1 == p.property1)).ToList();
As Except does not modify the list, you can use ForEach on List<T>:
list2.ForEach(item => list1.Remove(item));
It may not be the most efficient way, but it is simple, therefore readable, and it updates the original list (which is my requirement).
I think it would be quick to convert list A to a dictionary and then foreach the second list and call DictA.Remove(item) otherwise I think most solutions will cause many iterations through list A either directly or under the covers.
If the lists are small, it probably won't matter.
In case you have two different list with different DataModals
List<FeedbackQuestionsModel> feedbackQuestionsList = new();
List<EmployeesFeedbacksQuestionsModel> employeeQuestionsList = new();
var resultList = feedbackQuestionsList.Where(p => !employeeQuestionsList.Any(x => x.Question == p.Question)).ToList();
feedbackQuestionsList = resultList.ToList();
Here ya go..
List<string> list = new List<string>() { "1", "2", "3" };
List<string> remove = new List<string>() { "2" };
list.ForEach(s =>
{
if (remove.Contains(s))
{
list.Remove(s);
}
});
I have a List that has various derived classes. I may have something like this:
List<BaseClass> list = new List<BaseClass>() {
new Class1(),
new Class2(1),
new Class3(),
new Class2(2),
new Class4()
};
I am trying to use LINQ to semi-sort the list so that the natural order is maintained EXCEPT for Class2. All Class2 instances should be grouped together at the place that the first Class2 occurs. Here is what the output should be like:
List<BaseClass> list = new List<BaseClass>() {
new Class1(),
new Class2(1),
new Class2(2),
new Class3(),
new Class4()
};
I can't for the life of me figure out how to do this...
You can do it like this:
list = list
.TakeWhile(o => !(o is Class2))
.Concat(list.Where(o => o is Class2))
.Concat(
list.SkipWhile(o => !(o is Class2)).Where(o => !(o is Class2))
)
.ToList();
This will take all of the items until the first Class2 item, followed by all of the Class2 items, followed by all remaining non-Class2 items.