I get data from my db using linq. I would like to use a GroupBy and an OrderBy on the same Request.
I actually have this code which doesn't work:
var mydata = _db.table1
.Join(_db.table2, h => h.col1, t => t.col2,
(h, t) => new ActivatedScripts()
{
col1 = h.col1, col2 = h.col2, col3 = (t.col3 == "Y"), col4 = ""
})
.GroupBy(z => z.col1).OrderBy(s => s.....);
the OrderBy(s => s...) suggest me all the LINQ method and a famous KEY which doesn't match any column in my code.
EDIT :
I follow the official tutorial to sort my table (http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/sorting-filtering-and-paging-with-the-entity-framework-in-an-asp-net-mvc-application).
When I groupBy then sort (I tried to sort then groupby) I have an exception :
The GroupBy method returns a collection of groups. You can easily sort on the col1 column as that is the Key property of each group:
.OrderBy(s => s.Key)
If you want to sort on anything else, you have to get that value from the items in the group. If you for example know that a value is the same for all items in each group, you can get the value from the first item in the group:
.OrderBy(s => s.First().col2)
You can also use aggregates to calculate values using all the items in the group, for example sorting on the sum of the values:
.OrderBy(s => s.Sum(x => x.col2))
You can always order first and then group the ordered data:
.Join(...).OrderBy(x => x.col1).GroupBy(x => x.col2)
Related
I have a object list like below. I want to join every two rows into single row based on column B. It is sure that only two rows would be there for every single column B value.
Input
Output
However, I have done it and solution works. but I am looking for more better solution. I am not much happy with my solution.
My solution:
var groupByItems = items.GroupBy(x => x.ColumnB).Select(x => new MappingClass
{
ColumnA= x.FirstOrDefault().ColumnA,
ColumnB= x.FirstOrDefault().ColumnB,
ColumnC= x.Where(r=> !string.IsNullOrEmpty(r.ColumnC)).Select(r=>r.ColumnC).FirstOrDefault(),
ColumnD= x.Where(r => !string.IsNullOrEmpty(r.ColumnD)).Select(r => r.ColumnD).FirstOrDefault(),
}).ToList();
Now groupByItems object returns me two rows as expected.
You can use Key of the Groups generated by GroupBy()
Also, there's no need to use .Where() you can simply put your filter as a lambda expression in .FirstOrDefault() for ColumnC & ColumnD
var groupByItems = items.GroupBy(x => new { ColumnA = x.ColumnA, ColumnB = x.ColumnB })
.Select(x => new MappingClass
{
ColumnA = x.Key.ColumnA,
ColumnB = x.Key.ColumnB,
ColumnC = x.FirstOrDefault(m => !string.IsNullOrEmpty(m.ColumnC)).ColumnC,
ColumnD = x.FirstOrDefault(m => !string.IsNullOrEmpty(m.ColumnD)).ColumnD
})
.ToList();
I have a collection and I need to order it by descending date(DateProcessed field) using Linq, first I am grouping by two possible Keys: Booked or Empty. But the data it's not being ordered..
This is my expression:
IEnumerable<IGrouping<string, MyClassMongo>> sub = Model.MyCollection.GroupBy(f => f.IsBooked ? "Booked" : "Empty").OrderByDescending(f => f.FirstOrDefault().DateProcessed);
I'm confused because I am grouping first, I know that after grouping the collection is splitted in two(Booked and Empty) so I am not sure how to handle the sorting because I am grouping first
If you are querying in-memory collection, then just place ordering before grouping:
IEnumerable<IGrouping<string, MyClassMongo>> sub =
Model.MyCollection
.OrderByDescending(f => f.DateProcessed)
.GroupBy(f => f.IsBooked ? "Booked" : "Empty");
Items within each group will be sorted by DateProcessed.
if you want to first Group by and then sort the results within the Group. you can try some thing like below
Model.MyCollection
.GroupBy(f => f.IsBooked,
(f, g) => new{Key=f.DateProcessed, Group = g.OrderByDescending(c=>c.IsBooked)})
.OrderByDescending(f => f.Key);
PS: Code may have syntax issue not tested but the idea should be to create the key withing each group so we can order by
I am looking for a way in LINQ to get a max Id record by using 'Group By' clause
Consider the following Sample data
Table: ProcessAud
ProcessSeq ProjectSeq ProjectValue Active
11 1 50000 Y
12 1 10000 Y
13 2 70000 Y
14 2 90000 Y
In which I want to get two records as a list such that is second and fourth
records (i.e) ProcessSeq 12 and 14. And I tried it like following
var ProcessAudList = ProcessAudService.FilterBy(x => x.Active == "Y"
).GroupBy(x => x.ProjectSeq).Max().ToList();
It is not working properly, So how to do it in LINQ. Please anybody help.
You want to pick top record from each group.
var ProcessAudList = ProcessAudService.Where(x => x.Active == "Y")
.GroupBy(x => x.ProjectSeq, (key,g)=>g.OrderByDescending(e=>e.ProjectValue).First());
Check demo code
When you use GroupBy extension, method will return you IGrouping instance and you should query IGrouping instance like below;
var ProcessAudList = collection.Where(x => x.Active == "Y").GroupBy(x => x.ProjectSeq).Select(x => x.OrderByDescending(a => a.ProcessSeq).FirstOrDefault()).ToList();
Hope this helps
You're most of the way there, but Max is the wrong term to use.
Each IGrouping is an IEnumerable (or IQueryable) sequence of its own, so you can use OrderBy and First clauses to get the answer you need:
var ProcessAudList = ProcessAudService
.FilterBy(x => x.Active == "Y")
.GroupBy(x => x.ProjectSeq)
.Select(grp => grp.OrderByDescending(x => x.ProcessSeq).First())
.ToList();
The Select clause will process each of the groups, order the groups descending by ProcessSeq and select the first one. For the data you provided this will select the rows with ProcessSeq equal to 12 and 14.
With this code you can get all max id in foreach
var res = from pa in ProcessAud
group Cm by pa.ProjectSeq into Cm1
select new
{
_max = Cm1.Max(x => x.ProcessSeq)
};
foreach (var item in res)
{
//item._max have biggest id in group
}
Here is my code:
IEnumerable<ServiceTicket> troubletickets = db.ServiceTickets.Include(t => t.Company).Include(t => t.UserProfile);
var ticketGroups = new Dictionary<string, List<ServiceTicket>>();
ticketGroups = troubletickets
.GroupBy(o => o.DueDate).ToDictionary(
group => {
var firstOrDefault = #group.FirstOrDefault();
return firstOrDefault != null
? firstOrDefault.DueDate.HasValue
? firstOrDefault.DueDate.Value.ToShortDateString()
: ""
: "";
},
group => group.ToList()
).OrderBy(g => g.Key).ToDictionary(g => g.Key, g => g.Value);
The error that I am getting is: 'An item with the same key has already been added.' This is because the DueDate value is occasionally repeated. My question is how can I keep the key from being added if it already exists in the dictionary?
It seems that you are grouping by one value (the DueDate value), but using a different value as the dictionary key.
Can you not just use the custom code for grouping instead?
ticketGroups = troubletickets
.GroupBy(o => o.DueDate.HasValue
? o.DueDate.Value.ToShortDateString()
: "")
.ToDictionary(g => g.Key, g => g.ToList());
Note that I took our the superfluous OrderBy and second ToDictionary call - I assumed you were trying to "order" the dictionary which won't work as a plain dictionary is not ordered.
You get duplicate keys because there are two ways to get an empty string as key, either an empty group, or an empty date. The duplicate will always be the empty string. I wonder if you really intended to get an empty string as key when the group is empty. Anyway, it's not necessary, you can always filter empty groups later.
It's easier to group by date (including null) first through the database engine and then apply string formatting in memory:
IQueryable<ServiceTicket> troubletickets = db.ServiceTickets
.Include(t => t.Company)
.Include(t => t.UserProfile);
Dictionary<string, List<ServiceTicket>> ticketGroups =
troubletickets
.GroupBy(ticket => ticket.DueDate)
.AsEnumerable() // Continue in memory
.ToDictionary(g => g.Key.HasValue
? g.Key.Value.ToShortDateString()
: string.Empty,
g => g.Select(ticket => ticket));
Now the grouping is by the Key value, not by the First element in the group. The Key is never null, it's always a Nullable<DateTime>, with or without a value.
Side note: you'll notice that EF will not generate a SQL group by statement, that's because the SQL statement is "destructive": it only returns grouped columns and aggregate data, not the individual records that a LINQ GroupBy does return. For this reason, the generated SQL is pretty bloated and it may enhance performance if you place the AsEnumerable before the .GroupBy.
I need to convert my city list into group by state and order by city within it.
I tried below one but not able to get it right. Would appreciate any help on this.
cities.GroupBy(g => g.state).Select(o => o.OrderBy(c => c.cityname));
Try below code
cities.GroupBy(g => g.state)
.Select(o =>new {
State = o.Key,
Cities = o.OrderBy(c => c.cityname).Tolist()})
.Tolist();
cits.OrderBy(d => d.cityname).GroupBy(d => d.state).SelectMany(g => g).ToList();
1 - Order by cityname first.
2 - Then group them according to state. Since you order first, groups are still ordered with respect to cityname property.
3 - Convert to single list. Otherwise, you will end up with list of groups.
Should work. I also advice using camel case notation for naming your variables.
The ToLookup function may give you what you need.
cities.ToLookup(c => c.state, c => c.city);
This will create an IGrouping<string, string> where you can iterate through the Key values (states) and operate on a set of city values.
To sort it first, just do cities.OrderBy(c => c.state).ThenBy(c => c.city).
Do the orderby first:
cities.OrderBy(c=>c.cityname).GroupBy (c => c.state);
You might want to order the states to so.
cities.OrderBy(c=>c.cityname).GroupBy (c => c.state).OrderBy (g => g.Key);