I am using the SelectMany method to create a combination of items from two list of strings. I am able to create the flattended list without any issues, but unable to figure out how to add the index. In the example below, I need to assign the Position property of Product with the Index.
var strings = new List<string> { "Milk", "Eggs", "Cheese" };
var suffixes = new List<string> {"-Direct", "-InDirect"};
var products = strings
.SelectMany((_, index) => suffixes,
(x, y) => new Product {Position = ?, ID = x + y});
Thanks for any help,
You're specifying the index at the wrong place. You need it after the SelectMany. For example:
var products = strings.SelectMany(x => suffixex,
(x, y) => x + y)
.Select((id, index) => new Product { Position = index,
ID = id });
Related
Hi I have a List so:
A 1
A 2
A 3
A 4
B 1
B 2
C 1
I want to select the letter that contains AT LEAST these 3 numbers: 1,2,3
So in this case would be selected the letter A.
Can you help me to write this as LINQ expression?
Thanks a lot!
First, make a collection of the numbers you require.
var required = new[] { 1, 2, 3 };
Then, group your pairings by letter.
var groupedPairings = pairings.GroupBy(p => Letter, p => Number);
Then, discard those pairings that don't have your three required items. (The logic here is "take the collection of required items, remove anything in the group, and make sure there is nothing left".)
var groupsWithRequired = groupedPairings
.Where(g => !required.Except(g).Any());
Now, if you just want the letters, you can simply do
var lettersWithRequired = groupsWithRequired.Select(g => g.Key);
or if you want a dictionary mapping from the letter to its collection of numbers, you can do
var dictionary = groupsWithRequired.ToDictionary(g => g.Key, g => g.ToArray());
var numbersForA = dictionary["A"]; // = {1, 2, 3, 4}
You could try this, although I don't feel it's the best answer:
var items = new List<Item>{
new Item{Name="A", Value=1},
new Item{Name="A", Value=2},
new Item{Name="A", Value=3},
new Item{Name="A", Value=3},
new Item{Name="A", Value=4},
new Item{Name="B", Value=1},
new Item{Name="B", Value=2},
new Item{Name="C", Value=1},
};
var values = new List<int>{1,2,3};
var query = items.GroupBy (i => i.Name)
.Where (i => i.Select (x => x.Value)
.Intersect(values).Count() == values.Count)
.Select (i => i.Key);
Where
class Item{
public string Name{get;set;}
public int Value{get;set;}
}
I need to return all records (items) that has a part (X) so I can use that in a group or .GroupBy afterwards
Using this summary data:
ItemName PartName
1 A
1 B
2 A
3 C
So Item1 has two parts (A,B), etc...
I need a LINQ query that will
- find all items that have part A (i.e items 1 and 2)
- return all rows for all these items
1 A
1 B
2 A
Notice that the end result returned the row (1 B) because Item1 has PartA and so I need to get back all rows for Item1.
I was looking at something like:
let items = from data in summary where data.PartName == A select new { data.ItemName } // to get all the items I need
But then, now that I have that list I need to use it to get all the rows for all items listed, and I can't seem to figure it out ...
Actual Source Code (for reference):
NOTE:
Recipe = ITEM
Ingredient = PART
(I was just trying to make it simpler)
ViewFullRecipeGrouping = (
from data in ViewRecipeSummary
group data by data.RecipeName into recipeGroup
let fullIngredientGroups = recipeGroup.GroupBy(x => x.IngredientName)
select new ViewFullRecipe()
{
RecipeName = recipeGroup.Key,
RecipeIngredients = (
from ingredientGroup in fullIngredientGroups
select new GroupIngredient()
{
IngredientName = ingredientGroup.Key
}
).ToList(),
ViewGroupRecipes = (
from data in ViewRecipeSummary
// this is where I am looking to add the new logic to define something I can then use within the next select statement that has the right data based on the information I got earlier in this query.
let a = ViewRecipeSummary.GroupBy(x => x.RecipeName)
.Where(g => g.Any(x => x.IngredientName == recipeGroup.Key))
.Select(g => new ViewRecipe()
{
RecipeName = g.Key,
IngredientName = g.Select(x => x.IngredientName)
})
select new GroupRecipe()
{
// use the new stuff here
}).ToList(),
}).ToList();
Any help would be much appreciated.
Thanks,
I believe this does what you want:
var data = /* enumerable containing rows in your table */;
var part = "X";
var items = new HashSet<int>(data
.Where(x => x.PartName == part)
.Select(x => x.ItemName));
var query = data.Where(x => items.Contains(x.ItemName));
If I understand your comment at the end, I believe this also does what you want:
var query = data
.GroupBy(x => x.ItemName)
.Where(g => g.Any(x => x.PartName == part))
.Select(g => new
{
ItemName = g.Key,
PartNames = g.Select(x => x.PartName)
});
I have a newbie LINQ question. I need to create two objects of same type from a list of strings. I need to append a text 'Direct' & "Indirect' to the string and use them as ID to create the two unique objects.
var vStrings = new List { "Milk", "Eggs", "Cheese" };
var vProducts = (from s in vStrings
select new Product { ID = s + "-Direct" })
.Union(
from s in vStrings
select new Product { ID = s + "-InDirect" });
You can see in the example above, I am using a Union to create two different objects, Is there a better way to rewrite this LINQ query?
Thanks for your suggestions
If you ever needed more suffixes, this might be a better way:
var strings = new List<string> { "Milk", "Eggs", "Cheese" };
var suffixes = new List<string> {"-Direct", "-InDirect"};
var products = strings
.SelectMany(_ => suffixes, (x, y) => new Product() {ID = x + y});
And it would only iterate over the original set of strings once.
This way isn't much shorter but I think it would be a little better such as there is only one Concat instead of many Union:
var vProducts2 = (from s in vStrings
select s + "-Direct").Concat(
from s in vStrings
select s + "-InDirect");
I have the following LINQ conditional where clause query that produces a result of weights:
From this, I'd like to take the result set and join on another table, tblPurchases
var result = weights.Join(getsuppliersproducts.tblPurchases,
w => new { w.MemberId, w.MemberName, w.LocationId, w.UnitId },
p => new { p.MemberId, p.MemberName, p.LocationId, p.UnitId },
(w, p) => p);
In this second table, I have two columns I would like to perform an aggreagte function on, a sum on PurchaseQuantity and a count of UnitID.
So in its raw format, tblPurchases would look like so:
MemberID LocationID UnitId SupplierID SupplierStatus Purchases
1 1 ab Sup1 Live 10
1 1 abc Sup1 Live 10
1 1 abcd Sup2 Dead 50
From my results data set, I would like the output to look like so:
MemberID LocationID SupplierID SupplierStatus UnitIdCount Total Purchases
1 1 Sup1 Live 2 50
Also, with these amendments, can I still return this to a List?
How do I implement this using LINQ? I have tried, and failed miserably.
(To those who have seen my previous posts, I'm trying to cover all angles so I can fully understand the concept of what is going on in both SQL and LINQ)
That query will return an IEnumerable where each of the Purchases matches the MemberId, MemberName, LocationId and UnitId in the original Weights query. You can only easily do one aggregate at a time, so
var result = weights.Join(getsuppliersproducts.tblPurchases,
w => new { w.MemberId, w.MemberName, w.LocationId, w.UnitId },
p => new { p.MemberId, p.MemberName, p.LocationId, p.UnitId },
(w, p) => p).ToList();
Int32 count = result.Count();
Double quantity = result.Sum(p => p.PurchaseQuantity);
Is that what you're trying to do?
EDIT, after your reply of I would like to reutrn a list of tblPurchases with two new columns, the sum of Purchase Quantity and count of unit ID.
This gives a flat output:
var query = Weights.GroupJoin(
Purchases,
w => new {w.MemberId, w.LocationId},
p => new {p.MemberId, p.LocationId},
(w,p) => new {w.MemberId, w.LocationId, Count = p.Count(), Sum = p.Sum(x => x.Purchases)} );
Note that at the point we do the (w, p) => new {} that w is a single Weight and p is a list of Purchases matching that weight, so you can still keep all of teh (hierarchical) data:
var query = Weights.GroupJoin(
Purchases,
w => new {w.MemberId, w.LocationId},
p => new {p.MemberId, p.LocationId},
(w,p) => new {w.MemberId, w.LocationId, Count = p.Count(), Sum = p.Sum(x => x.Purchases), Purchases = p} );
How can I join 2 lists of equal lengths (to produce a 3rd list of equal length) where I do not want to specify a condition but simply rely on the order of items in the 2 lists.
Eg how can I join:
{1,2,3,4} with {5,6,7,8}
to produce:
{{1,5}, {2,6}, {3,7}, {4,8}}
I have tried the following:
from i in new []{1,2,3,4}
from j in new []{5,6,7,8}
select new { i, j }
but this produces a cross join. When I use join, I always need to specify the "on".
You could use Select in the first list, use the item index and access the element on the second list:
var a = new [] {1,2,3,4};
var b = new [] {5,6,7,8};
var qry = a.Select((i, index) => new {i, j = b[index]});
If you are using .Net 4.0, you can use the Zip extension method and Tuples.
var a = new [] {1,2,3,4};
var b = new [] {5,6,7,8};
var result = a.Zip(b, (an, bn) => Tuple.Create(an, bn));
Alternatively, you can keep them as arrays:
var resultArr = a.Zip(b, (an, bn) => new []{an, bn});
There is a half way solution, if you want to use query syntax. Half way in the sense that you need to use the Select method on both lists in order to get the indexes that you will use in the where clause.
int[] list1 = {1,2,3,4};
int[] list2 = {5,6,7,8};
var result = from item1 in list1.Select((value, index) => new {value, index})
from item2 in list2.Select((value, index) => new {value, index})
where item1.index == item2.index
select new {Value1 = item1.value, Value2 = item2.value};
The benefit with this solution is that it wont fail if the lists have different lengths, as the solution using the indexer would do.