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LINQ: select specific value in a datatable column

In table I have 4 Columns GroupName, Display, Value and ID
How can I just show a specific data in display. I only want to show some of the groupNames Data
for example I only want to show Groupname = company and display = Forbes
Here's my linq
sample = (from c in smsDashboardDBContext.CodeDefinitions
orderby c.Display ascending
select new CodeDefinitionDTO
{
GroupName = c.GroupName,
Display = c.Display,
Value = c.Value,
Id = c.Id
}).ToList();

You can add a where statement in the query.
where c.GroupName == "company" && c.Display == "Forbes"

I only want to show some of the groupNames Data for example I only want to show Groupname = company and display = Forbes
Before the ToList, use a Where to keep only those items that you want to show:
var company = ...
var forbes = ...
var result = smsDashboardDBContext.CodeDefinitions
.OrderBy(codeDefinition => codeDefintion.Display)
.Select(codeDefinition => new CodeDefinitionDTO
{
Id = codeDefinition.Id,
GroupName = codeDefinition.GroupName,
Display = codeDefinition.Display,
Value = codeDefinition.Value,
})
.Where(codeDefinition => codeDefition.GroupName == company
&& codeDefintion.Display == forbes);
In words:
Order all codeDefinitions that are in the table of CodeDefintions by ascending value of property codeDefintion.Display.
From every codeDefinition in this ordered sequence make one new CodeDefinitionDTO with the following properties filled: Id, GroupName, Display, Value
Frome every codeDefintion in this sequence of CodeDefinitionDTOs, keep only those codeDefinitions that have a value for property GroupName that equals company and a value for property Display that equals forbes.
There is room for improvement!
Suppose your table has one million elements, and after the Where, only five elements are left. Then you will have sorted almost one million elements for nothing. Consider to first do the Where, then the Order and finally a Select.
In LINQ, try to do aWhere as soon as possible: all following statements will have to work on less items
In LINQ, try to do a Select as late as possible, preferrably just before the ToList / FirstOrDefault / ... This way the Select has to be done for as few elements as possible
So first the Where, then the OrderBy, then the Select, and finally the ToList / FirstOrDefault, etc:
var result = smsDashboardDBContext.CodeDefinitions
.Where(codeDefinition => ...);
.OrderBy(codeDefinition => codeDefintion.Display)
.Select(codeDefinition => new CodeDefinitionDTO
{
...
});

How can I convert this linq to bool

How to convert a query to bool?
I used the "ALL (x => x)" but did not give the answer I needed.
Code Line
checkItemInventory.Where(x => listCost.Contains(x.Id));
In this case, the listcost would have 2 items, I needed to check if the checkItemInventory has these 2 items.

"All items in the inventory have an id that present in listcost". listCost needs to have the same number of items as inventory (assuming Id is unique) possibly more, to stand a chance of returning true
checkItemInventory.All(x => listCost.Contains(x.Id))
"At least one item in the inventory has an id that is also in listCost". Listcost could minimally have only one id in it, to stand a chance of returning true
checkItemInventory.Any(x => listCost.Contains(x.Id))
As you can see, neither of these are what you want as you seem to be saying you want to check whether every item in listcost is also present in the inventory. This is like the top code, but the other way round ("all items in listCost are present in inventory" vs "all items in inventory are present in listcost"
I think I'd make a dictionary out of the inventory first, unless it's already something that supports a fast lookup:
var d = checkItemInventory.Select(x => new { x.Id, x.Id }).ToDictionary();
var boolResult = listCost.All(lc => d.ContainsKey(lc));
If inventory is small, you could use this approach:
listCost.All(lc => checkItemInventory.Any(cii => cii.Id == lc));
Just be mindful that internally it might do something like:
bool all = true;
foreach(lc in listCost){
bool found = false;
foreach(cci in checkItemInventory)
if(lc == cci.Id){
found = true;
break;
}
all &= found;
if(!all)
return false;
}
return true;
Which is a lot of repeated comparisons (for every item in listCost, the whole inventory is scanned), could be slow
Edit
I asked for clarification of how you store your inventory and your costs of building items. Here's one assumption I made, and how a solutio based on it might work:
Assuming your inventory has the kind of item and a count saying how many of that item the player is carrying:
class InventoryItem{
int ItemKindId { get; set;}
int CountOf { get; set; }
}
player.Inventory.Add(new InventoryItem() {
ItemKindId = Constants.WOOD, //1
CountOf = 10 //holding 10 items of wood
};
player.Inventory.Add(new InventoryItem() {
ItemKindId = Constants.STONE, //2
CountOf = 5 //holding 5 items of stone
};
Assuming you have a Recipe for making e.g. an axe, it needs 1 wood and 2 stone, but it lists them in simple order:
int[] axeRecipe = new int[] { Constants.WOOD, Constants.STONE, Constants.STONE };
Might be easiest to group the recipe:
var recipe = axeRecipe.GroupBy(item => item)
/*
now we have a grouping of the recipe[item].Key as the material and a
recipe[item].Count() of how much. The group is like a dictionary:
recipe[Constants.WOOD] = new List<int>{ Constants.WOOD };
recipe[Constants.STONE] = new List<int>{ Constants.STONE, Constants.STONE, };
A group item has a Key and a list of objects that have that key
Because my recipe was simply ints, the Key is the same number as all the
items in the list
*/
//for all items in the recipe
grp.All(groupItem =>
//does the player inventory contain any item
playerInventory.Any(inventoryItem =>
//where the material kind is the same as the recipe key (material)
inventoryItem.ItemKindId == groupItem.Key &&
//and the count they have of it, is enough to make the recipe
inventoryItem.CountOf >= groupItem.Count()
);
You can of course reduce this to a single line if you want: axeRecipe.GroupBy(...).All(...)

You could map the listCost to a list of int and then use Except() and Any() to check whether all items are contained:
bool containsAll = !listCost.Select(x => x.Id).Except(checkItemInventory).Any();

[UPDATE]
You are telling us the following:
How to convert a query to bool? I used the "ALL (x => x)" but did not give the answer I needed.
checkItemInventory.Where(x => listCost.Contains(x.Id));
In this case, the listcost would have 2 items, I needed to check if
the checkItemInventory has these 2 items.
if you need to check if there is any result then you can use:
bool hasItems = checkItemInventory.Where(x => listCost.Contains(x.Id)).Any();
if you need to count the result you can use
checkItemInventory.Where(x => listCost.Contains(x.Id)).Count();

You could use a Join to create a method based Linq query and use the results to check if the length of the list is greater than 0. Then turn that into a boolean.
var query = checkItemInventory.Join(listCost,
inventory => inventory.Id,
cost => cost.Id,
(inventory, cost) => new { id = inventory.Id });
var count = query.ToList().Count();
var b = (count > 0);

If I get it correctly, listCost can have less elements than checkItemInventory. You want to check that all elements in listCost have a corresponding element in checkItemInventory. Correct? If yes, try this:
listCost.All(x => checkItemInventory.Contains(x));
I don't know the type of these lists, so you might need to use x.id in some places

Getting only the highest value in the database

public ActionResult List_of_Winners(int id=0)
{
var winners = (from cat in db.Events_Category_tbl
join can in db.Candidates_Info_tbl
on cat.events_category_id equals can.events_category_id
where cat.events_info_id == id
select new Candidates
{
events_category_name = cat.events_category_name,
candidates_fullname = can.candidates_fullname,
candidates_info_id = can.candidates_info_id,
events_category_id = cat.events_category_id,
no_of_votes = can.no_of_votes.Value
}).OrderBy(x => x.no_of_votes).Distinct();
return PartialView(winners);
}
I have 2 tables, the Events_Category_tbl & Candidates_Info_tbl then in one category there are many candidates registered. Then, what I want to do is that I need to get only the highest votes in the category. And this serve as the winner of the category.
My Candidates table looks like this:
candidates_info_id,
candidates_fullname,
events_category_id,
no_of_votes
My Category table looks this way:
events_category_id,
events_category_name
Then, I want a result in my query that in one category it has one winner of the candidates the one got the highest votes.
How am I gonna do that?
Above is my code.

How do I Pick the best performer from a set using LINQ

Given a set var battingContribution = IQueryable<Player, Runs> (Basically a list of players and their total batting score) and another set var bowlingContribution = IQueryable<Player, Runs>, how do I pick whose net contribution was the best such that the player whose batting score minus the bowling score results in the highest net total?

Assuming that you have IDictionary<Player, Runs> instead of IQueryable (which doesn't have two type parameters):
// Just to make sure that we don't get exceptions if a player is only in one
// of the two collections -- you might want to handle this case differently
var players = battingContribution.Keys.Intersect(bowlingContribution.Keys);
// Put each player and their performance into what is essentialy a tuple
var performance = players.Select(p =>
new {
Player = p,
Performance = battingContribution[p] - bowlingContribution[p]
});
// Sorting
var orderedPerformance = performance.OrderByDescending(item => item.Performance);
// Selecting best performer
var bestPerformer = orderedPerformance.First().Player;
You can chain these together for terseness if you prefer.

The following works only for Players that are in both Contributions (although I don't know an IQueryable with two type params):
var BestPlayer = (from a in (from bt in battingContribution from bw in BowlingContribution where bt.Player == bw.Player select new { Player = bt.Player, Diff = bt.Runs - bw.Runs)) orderby a.Diff descending select a).First().Player;
MSDN reference to Linq samples see http://msdn.microsoft.com/en-us/vcsharp/aa336746
EDIT - as per comment from OP for completeness:
var BestPlayer = (from a in (from bt in batRuns from bw in bowlRuns where bt.Player == bw.Player select new { Player = bt.Player, Diff = bt.Runs - bw.Runs}) orderby a.Diff descending select a).First();

Filling in missing dates using a linq group by date query

I have a Linq query that basically counts how many entries were created on a particular day, which is done by grouping by year, month, day. The problem is that because some days won't have any entries I need to back fill those missing "calendar days" with an entry of 0 count.
My guess is that this can probably be done with a Union or something, or maybe even some simple for loop to process the records after the query.
Here is the query:
from l in context.LoginToken
where l.CreatedOn >= start && l.CreatedOn <= finish
group l by
new{l.CreatedOn.Year, l.CreatedOn.Month, l.CreatedOn.Day} into groups
orderby groups.Key.Year , groups.Key.Month , groups.Key.Day
select new StatsDateWithCount {
Count = groups.Count(),
Year = groups.Key.Year,
Month = groups.Key.Month,
Day = groups.Key.Day
}));
If I have data for 12/1 - 12/4/2009 like (simplified):
12/1/2009 20
12/2/2009 15
12/4/2009 16
I want an entry with 12/3/2009 0 added by code.
I know that in general this should be done in the DB using a denormalized table that you either populate with data or join to a calendar table, but my question is how would I accomplish this in code?
Can it be done in Linq? Should it be done in Linq?

I just did this today. I gathered the complete data from the database and then generated a "sample empty" table. Finally, I did an outer join of the empty table with the real data and used the DefaultIfEmpty() construct to deal with knowing when a row was missing from the database to fill it in with defaults.
Here's my code:
int days = 30;
// Gather the data we have in the database, which will be incomplete for the graph (i.e. missing dates/subsystems).
var dataQuery =
from tr in SourceDataTable
where (DateTime.UtcNow - tr.CreatedTime).Days < 30
group tr by new { tr.CreatedTime.Date, tr.Subsystem } into g
orderby g.Key.Date ascending, g.Key.SubSystem ascending
select new MyResults()
{
Date = g.Key.Date,
SubSystem = g.Key.SubSystem,
Count = g.Count()
};
// Generate the list of subsystems we want.
var subsystems = new[] { SubSystem.Foo, SubSystem.Bar }.AsQueryable();
// Generate the list of Dates we want.
var datetimes = new List<DateTime>();
for (int i = 0; i < days; i++)
{
datetimes.Add(DateTime.UtcNow.AddDays(-i).Date);
}
// Generate the empty table, which is the shape of the output we want but without counts.
var emptyTableQuery =
from dt in datetimes
from subsys in subsystems
select new MyResults()
{
Date = dt.Date,
SubSystem = subsys,
Count = 0
};
// Perform an outer join of the empty table with the real data and use the magic DefaultIfEmpty
// to handle the "there's no data from the database case".
var finalQuery =
from e in emptyTableQuery
join realData in dataQuery on
new { e.Date, e.SubSystem } equals
new { realData.Date, realData.SubSystem } into g
from realDataJoin in g.DefaultIfEmpty()
select new MyResults()
{
Date = e.Date,
SubSystem = e.SubSystem,
Count = realDataJoin == null ? 0 : realDataJoin.Count
};
return finalQuery.OrderBy(x => x.Date).AsEnumerable();

I made a helper function which is designed to be used with anonymous types, and reused in as generic way as possible.
Let's say this is your query to get a list of orders for each date.
var orders = db.Orders
.GroupBy(o => o.OrderDate)
.Select(o => new
{
OrderDate = o.Key,
OrderCount = o.Count(),
Sales = o.Sum(i => i.SubTotal)
}
.OrderBy(o => o.OrderDate);
For my function to work please note this list must be ordered by date. If we had a day with no sales there would be a hole in the list.
Now for the function that will fill in the blanks with a default value (instance of anonymous type).
private static IEnumerable<T> FillInEmptyDates<T>(IEnumerable<DateTime> allDates, IEnumerable<T> sourceData, Func<T, DateTime> dateSelector, Func<DateTime, T> defaultItemFactory)
{
// iterate through the source collection
var iterator = sourceData.GetEnumerator();
iterator.MoveNext();
// for each date in the desired list
foreach (var desiredDate in allDates)
{
// check if the current item exists and is the 'desired' date
if (iterator.Current != null &&
dateSelector(iterator.Current) == desiredDate)
{
// if so then return it and move to the next item
yield return iterator.Current;
iterator.MoveNext();
// if source data is now exhausted then continue
if (iterator.Current == null)
{
continue;
}
// ensure next item is not a duplicate
if (dateSelector(iterator.Current) == desiredDate)
{
throw new Exception("More than one item found in source collection with date " + desiredDate);
}
}
else
{
// if the current 'desired' item doesn't exist then
// create a dummy item using the provided factory
yield return defaultItemFactory(desiredDate);
}
}
}
The usage is as follows:
// first you must determine your desired list of dates which must be in order
// determine this however you want
var desiredDates = ....;
// fill in any holes
var ordersByDate = FillInEmptyDates(desiredDates,
// Source list (with holes)
orders,
// How do we get a date from an order
(order) => order.OrderDate,
// How do we create an 'empty' item
(date) => new
{
OrderDate = date,
OrderCount = 0,
Sales = 0
});
Must make sure there are no duplicates in the desired dates list
Both desiredDates and sourceData must be in order
Because the method is generic if you are using an anonymous type then the compiler will automatically tell you if your 'default' item is not the same 'shape' as a regular item.
Right now I include a check for duplicate items in sourceData but there is no such check in desiredDates
If you want to ensure the lists are ordered by date you will need to add extra code

Essentially what I ended up doing here is creating a list of the same type with all the dates in the range and 0 value for the count. Then union the results from my original query with this list. The major hurdle was simply creating a custom IEqualityComparer. For more details here: click here

You can generate the list of dates starting from "start" and ending at "finish", a then step by step check the number of count for each date separately