I have 2 lists.
They are different in length but same type.
I want that an Item from List2 replaces an equal item in List1.
var item1 = new Item { Id = 1, Name = "Test1" };
var item2 = new Item { Id = 2, Name = "Test2" };
var item3 = new Item { Id = 3, Name = "Test3" };
var item4 = new Item { Id = 4, Name = "Test4" };
var item5 = new Item { Id = 5, Name = "Test5" };
var list1 = new List<Item> { item1, item2, item3, item4, item5 };
var list2 = new List<Item> { new Item { Id = 1, Name = "NewValue" } };
As a result I expect a list with 5 items where the item with Id = 1 has a value "NewValue".
How can I do that preferable with linq.
UPDATE
I extend my question:
How can the replacement of the replaced Item happen without copying all properties manually. Just imagine I have 100 properties...
This is one way to do it:
First define an equality comparer that depends only on the Id property of the Item class like this:
public class IdBasedItemEqualityComparer : IEqualityComparer<Item>
{
public bool Equals(Item x, Item y)
{
return x.Id == y.Id;
}
public int GetHashCode(Item obj)
{
return obj.Id.GetHashCode();
}
}
Then you can take items list1 that don't have corresponding items in list2 using the Except method and then you can concatenate that with list2 using the Concat method like this:
var result = list1.Except(list2, new IdBasedItemEqualityComparer()).Concat(list2).ToList();
Notice how I use the IdBasedItemEqualityComparer with the Except method, so that comparison is based only on Id.
Off the top of my head this is one solution
var list3 = new List<Item>();
foreach (var item in list1)
list3.Add(list2.FirstOrDefault(s => s.Id == item.Id) ?? item);
I think LEFT OUTER JOIN in Linq will be able to merge 2 lists regardless of number of properties(columns) like this:
List<Item> newItems =
(from l1 in list1
join l2 in list2 on l1.Id equals l2.Id into l12
from l2 in l12.DefaultIfEmpty()
select new { Item = (l2 == null) ? l1 : l2 }).Select(r => r.Item).ToList();
Related
I was looking to get items from ListA, where the value of Id is same in both of the lists, and the count of Id must be more than 1 in list A or list B
var items = itemsA.Where(x => itemsB.Select(y => y.Id == x.Id).Count() > 1);
This gives me the result where same Ids in itemsB is more then 1, I want to use a or condition to check for the same counter in itemsA
Eg 1:
ListA=[{"id"=1,"name="abc"},{"id=1, "name"="def"}]
ListB=[{"id=2","name="xyz"}, {"id=1, "name"="mno"}]
Should return [{"id"=1,"name="abc"},{"id=1, "name"="def"}] because id =1 exists in listB and the count of id with value 1 in listA is more then 1.
Eg 2:
ListA=[{"id"=2,"name="abc"},{"id=1, "name"="def"}]
ListB=[{"id=1","name="xyz"}, {"id=1, "name"="mno"}]
should return {"id=1, "name"="def"} because common id in both list is 1 and the count of id with value 1 in ListB is more then 1.
I am not certain this is the best solution, but as far as I've understood the question, it should be a solution.
Assuming you have an Item class as follows:
public class Item
{
public int Id { get; set; }
public string Name { get; set; }
}
and define itemsA and itemsB as List<Item>s, you can first find all Ids that are present in both lists, then select the applicable items from itemsA based on occurrence of each Id in either list:
IEnumerable<int> idsInBothItemLists = itemsA
.Select(a => a.Id)
.Intersect(itemsB.Select(b => b.Id))
.Distinct();
List<Item> items = itemsA
.Where(a => idsInBothItemLists.Contains(a.Id))
.GroupBy(a => a.Id)
.Where(gr =>
gr.Skip(1).Any() ||
itemsB.Where(b => b.Id == gr.Key).Skip(1).Any())
.SelectMany(gr => gr.Select(item => item))
.ToList();
(.Skip(1).Any() serves the same purpose as .Count() > 1 in your original code; it simply checks whether there are any items left after skipping the first item.)
Printing the output from the suggested population of itemsA and itemsB
foreach (var entry in items)
{
Console.WriteLine(entry.Id + " " + entry.Name);
}
e.g. for input
var itemsA = new List<Item>
{
new Item { Id = 1, Name = "abc" },
new Item { Id = 3, Name = "def" },
new Item { Id = 1, Name = "ghi" },
new Item { Id = 2, Name = "jkl" }
};
var itemsB = new List<Item>
{
new Item { Id = 2, Name = "xyz" },
new Item { Id = 2, Name = "jkl" },
new Item { Id = 1, Name = "mno" },
new Item { Id = 3, Name = "pqr" }
};
gives
1 abc
1 ghi
2 jkl
I have a List which is populated with data from a database.
The object array has say 10 elements when populated
I want to do a LINQ Select Statement that gets returns a List<object[]> with just 2 elements. How can I select these elements 1 and 2.
I have tried the following which work for element 0 but How can I get element 0 and element 1 ??
var resultDistinct = result.Select(p => p.GetValue(0)).Distinct();
var resultDistinct2 = result.Select(p => p.ElementAt(0)).Distinct();
You could use an anonymous object for this..
var items = result.Select(p => new { ValueA = p.GetValue(0), ValueB = p.GetValue(1) });
Then access each item
foreach(var item in items)
{
var valueA = item.ValueA;
var valueB = item.ValueB;
}
You can use the Take extension method:
items.Take(x);
This will return the first x items of a collection.
If you want to skip over some elements, you can use Skip(x) before calling Take. These two methods are very often used for paging.
If you want distinct and then 2 then,
result.Select(p => p).Distinct().Take(2);
If just 2 then,
result.Take(2);
private class Foo
{
public int Item1;
public int Item2;
public int Item3;
}
static void Main(string[] args)
{
List<Foo> foos = new List<Foo>
{
new Foo() { Item1 = 1, Item2 = 2, Item3 = 3 },
new Foo() { Item1 = 4, Item2 = 5, Item3 = 6 },
new Foo() { Item1 = 7, Item2 = 8, Item3 = 9 }
};
// Create a list of lists where each list has three elements corresponding to
// the values stored in Item1, Item2, and Item3. Then use SelectMany
// to flatten the list of lists.
var items = foos.Select(f => new List<int>() { f.Item1, f.Item2, f.Item3 }).SelectMany(item => item).Distinct();
foreach (int item in items)
Console.WriteLine(item.ToString());
Console.ReadLine();
}
refer to: https://nickstips.wordpress.com/2010/09/16/linq-selecting-multiple-properties-from-a-list-of-objects/
Currently, I have implemented two lists with a double for loop to find matches between the two lists so I can join on them.
I have a list A which contains an ID and some other columns. I have a list B which contains an ID and some other columns. I have currently implemented a for loop within a for loop in order to make the comparisons for all the IDs so that I can find the ones that match and then return the joined results. I know want to understand how to implement a dictionary in this case as that will be more efficient to fix this problem.
public IEnumerable<Details> GetDetails(string ID)
{
// there are two lists defined up here
for (var item in listA)
{
for (var item2 in listB)
{
if (item.ID == item2.ID)
{
item.Name = item2.name;
}
}
}
return results;
}
Instead of having this double for loop, which is very inefficient. I want to learn how to implement a dictionary to fix this problem.
The dictionary would use the ids as keys (or indexes) so
Dictionary<string, object> myListA = new Dictionary<string, object>();
Dictionary<string, object> myListB = new Dictionary<string, object>();
public object GetDetails(string ID)
{
object a = myListA[ID];
object b = myListB[ID];
// combine them here how you want
// object c = a + b;
return c;
}
How about using linq to achieve your actual requirement? Something like:
public IEnumerable<A> GetDetails(int ID)
{
var listA = new List<A>
{
new A(){ ID = 1, Name = 2 },
new A(){ ID = 3, Name = 4 },
new A(){ ID = 5, Name = 6 },
};
var listB = new List<B>
{
new B(){ X = 1, name = 0 },
new B(){ X = 3, name = 1 }
};
return listA.Join(listB, k => k.ID, k => k.ID, (item, item2) =>
{
item.Name = item2.name;
return item;
}).Where(w => w.ID == ID);
}
If you just want the common IDs in the two lists, you can achieve that like this:
var commonIds = listA.Select(o => o.ID).Intersect(listB.Select(o => o.ID));
I have a list of objects each containing a list of strings, and I want to use group objects that contain the same value within their lists.
I'm trying something like this, but it puts them all in the same lists.
List<Item> Items = new List<Item>();
Item Item1 = new Item();
Item1.Id = "1";
Item1.Names.AddRange(new List<string> { "A" });
Items.Add(Item1);
Item Item2 = new Item();
Item2.Id = "2";
Item2.Names.AddRange(new List<string> { "B" });
Items.Add(Item2);
Item Item3 = new Item();
Item3.Id = "3";
Item3.Names.AddRange(new List<string> { "A", "C" });
Items.Add(Item3);
List<List<Item>> GroupedItems = Items.GroupBy(u => u.Names.GroupBy(s => s)).Select(t => t.ToList()).ToList();
What I would like to have happen in this scenario is GroupedItems contains two lists, the first contains Item1and Item3, the second contains Item2.
List<List<Item>> GroupedItems = Items
// Select only distinct names that can occur
.SelectMany(x => x.Names).Distinct()
// For every unique name find items that have it in Names
.Select(name => Items.Where(x => x.Names.Contains(name)).ToList())
.ToList();
I have a generic list:
List<Test> lstReport = new List<Test>();
lstReport.Add(new Test { ID = 1, Category = "Hot work", Approver = "Praveen" });
lstReport.Add(new Test { ID = 1, Category = "Civil work", Approver = "Praveen" });
lstReport.Add(new Test { ID = 1, Category = "Others", Approver = "Praveen" });
lstReport.Add(new Test { ID = 4, Category = "Hot work", Approver = "Praveen" });
lstReport.Add(new Test { ID = 5, Category = "Critical work", Approver = "Praveen" });
Now I want to take unique rows from the generic list by the ID value.
For eg, I need to group the rows having same ID and if the existence of ID's more than once, then its Category field has to be changed to "Grouped".
How can I write this expression?
This Works:
var QueryResult = (from x in lstReport
group x by x.ID into res
select new Test
{
ID = res.Key,
Category = res.Count() > 1 ? "Grouped" : res.First().Category,
Approver = res.First().Approver
}).ToList();
List<Test> lstReport = new List<Test>();
...
var groups = lstReport.GroupBy(i => i.ID).ToList();
foreach(var group in groups) {
var items = group.ToList();
if(items.Count > 1)
items.ForEach(i => { i.Category = "Grouped"; });
}
You can try this
var q = from r in lstReport
group r by r.ID into g
select new Test{ID=g.Key, Category = g.Count()>1? "Grouped" : g.Min(Category)};
also you can have g.Max(...) or g.Min(...)
You can use Linq to group objects based on some property:
var list = lstReport.GroupBy(t => t.ID);
This will return a new collection with 3 items: IEnumerable<IGrouping<TKey, TSource>>; which basically means a collection containing a collection with one or more items.
Then you can iterate over that new collection and check if each item contains more than one subitem; if it does, then iterate over the subitems and modify the Category value.
http://msdn.microsoft.com/en-us/library/system.linq.enumerable.groupby(v=vs.110).aspx