I am trying to use LINQ to create a Dictionary<string, List<CustomObject>> from a List<CustomObject>. I can get this to work using "var", but I don't want to use anonymous types. Here is what I have
var x = (from CustomObject o in ListOfCustomObjects
group o by o.PropertyName into t
select t.ToList());
I have also tried using Cast<>() from the LINQ library once I have x, but I get compile problems to the effect of it being an invalid cast.
Dictionary<string, List<CustomObject>> myDictionary = ListOfCustomObjects
.GroupBy(o => o.PropertyName)
.ToDictionary(g => g.Key, g => g.ToList());
I cannot comment on #Michael Blackburn, but I guess you got the downvote because the GroupBy is not necessary in this case.
Use it like:
var lookupOfCustomObjects = listOfCustomObjects.ToLookup(o=>o.PropertyName);
var listWithAllCustomObjectsWithPropertyName = lookupOfCustomObjects[propertyName]
Additionally, I've seen this perform way better than when using GroupBy().ToDictionary().
For #atari2600, this is what the answer would look like using ToLookup in lambda syntax:
var x = listOfCustomObjects
.GroupBy(o => o.PropertyName)
.ToLookup(customObject => customObject);
Basically, it takes the IGrouping and materializes it for you into a dictionary of lists, with the values of PropertyName as the key.
This might help you if you to Get a Count of words. if you want a key and a list of items just modify the code to have the value be group.ToList()
var s1 = "the best italian resturant enjoy the best pasta";
var D1Count = s1.ToLower().Split(' ').GroupBy(e => e).Select(group => new { key = group.Key, value = group.Count() }).ToDictionary(e => e.key, z => z.value);
//show the results
Console.WriteLine(D1Count["the"]);
foreach (var item in D1Count)
{
Console.WriteLine(item.Key +" "+ item.Value);
}
The following worked for me.
var temp = ctx.Set<DbTable>()
.GroupBy(g => new { g.id })
.ToDictionary(d => d.Key.id);
Related
Linq newbie here, struggling with my first GroupBy query.
I have a list of objects of type KeywordInstance which represents a keyword, and the ID of the database record to which the keyword was applied.
Keyword RecordID
macrophages 1
macrophages 2
cell cycle 3
map kinase 2
cell cycle 1
What I want is a collection of all keywords, with a list of the RecordIDs to which each keyword was applied.
Keyword RecordIDs
macrophages 1, 2
cell cycle 1, 3
map kinase 2
I tried using Linq to get it into a new object. I only managed to get the distinct keywords.
var keywords = allWords
.GroupBy(w => w.keyword)
.Select(g => new {keyword = g.Key});
The problem is that I can't seem to get the values of g in any way. g is of the type IGrouping<String, KeywordInstance> and by documentation, it only has the property Key, but not even the property Value. All the examples I have seen on the Internet for groupby just tell me to select g itself, but the result of
var keywords = allWords
.GroupBy(w => w.keyword)
.Select(g => new {keyword = g.Key, RecordIDs = g});
is not what I want.
Any try to get something out of g fails with the error message System.Linq.IGropuing<string, UserQuery.KeywordInstance> does not have a definition for [whatever I tried].
What am I doing wrong here?
I think you are close to you solution.
var keywords = allWords
.GroupBy(w => w.keyword)
.Select(g => new
{
keyword = g.Key,
RecordIDs = g.Select(c => c.ID)
});
Just Select the records you need.
The reason you are seeing the Keyword-column as well as the ID-column, is becuase it's part of g
var keywords = allWords.GroupBy(w => w.keyword);
foreach (var itm in keywords)
{
var list = itm.ToList();
//list returns all of the original properties/values objects from allwords.
//itm.key returns w.keyword
}
am a newbie in linq.. am stuck with one scenario. ie,
i have to sort the search results based on user input.
user inputs are Last Name, First Name and Title. for input 3 drop downs are there and i have to sort result based on the values selected.
i tried
order = Request["orders"].Split(',');
var param = order[0];
var p1 = typeof(Test).GetProperty(param);
param = order[1];
var p2 = typeof(Test).GetProperty(param);
param = order[2];
var p3 = typeof(Test).GetProperty(param);
model.Test = (from tests in model.Test
select tests).
OrderBy(x => p1.GetValue(x, null)).
ThenBy(x => p2.GetValue(x, null)).
ThenBy(x => p3.GetValue(x, null));
but it doesn't works.
i want qry like this
from tests in model.Test
select tests).OrderBy(x => x.lastname).
ThenBy(x => x.firstname).ThenBy(x => x.Title);
order[0]== lastname but how can i use it in the place of OrderBy(x => x.order[0])..?
Thanks in advance.
i solved my case as follows
// list of columns to be used for sorting
List<string>order = Request["orders"].Split(',').ToList();
//map the column string to property
var mapp = new Dictionary<string, Func<Test, string>>
{
{"FirstName", x => x.FirstName},
{"LastName", x => x.LastName},
{"SimpleTitle", x => x.SimpleTitle}
};
//user inputted order
var paras = new List<Func<Test, string>>();
foreach (var para in order)
{
if(!string.IsNullOrEmpty(para))
paras.Add(mapp[para]);
}
//sorting
model.Test= model.Test.OrderBy(paras[0]).ThenBy(paras[1]).ThenBy(paras[2]);
Thanks all,
Actually you are looking for dynamic linq query than you can try out Dynamic LINQ (Part 1: Using the LINQ Dynamic Query Library)
which allow to do like this
it means you can dynamically pass string propertyname to short you collection in orderby function
You can also read about : Dynamic query with Linq
You can compose the expression (any Expression) manually from pieces and then append it to the previous part of query. You can find more info, with example in "Sorting in IQueryable using string as column name".
I have a LINQ query where I want to select and read the p.Api value.
var api = DataAccessNew.Instance.dcServers.Where(p => p.Ip == IpAddress).Select(p => p.Api);
How do I read the p.Api value?
I have tried api.ToString() but I get SQL instead of actual column value.
You are getting an IEnumerable<> back (and your ToString call is showing you the value of that expression).
If you are expecting a single value, do this:
var api = DataAccessNew.Instance.dcServers
.Where(p => p.Ip == IpAddress)
.Select(p => p.Api)
.Single();
You might be interested to read about the other methods like Single(): SingleOrDefault, First, FirstOrDefault. Which one you used depends on whether you are expecting a single or multiple values returned (Single vs. First) and what you want to happen if there are no values (the *Default methods will return the type default instead of throwing an exception).
Or if you want to look at all the returned values:
var api = DataAccessNew.Instance.dcServers
.Where(p => p.Ip == IpAddress)
.Select(p => p.Api);
foreach (var apiValue in api)
{
// apiValue will have the value you're looking for.
}
Try this snippet of code:
string apiValue = api.FirstOrDefault().ToString();
your syntex seems ok..
By the way try this
string api =DataAccessNew.Instance.dcServers.Where(p => p.Ip == IpAddress).Select(p => p.Api).FirstOrDefault();
if p.Ip is a unique key in your table you could try to add .FirstOrDefault() after your Linq query.
public string getselectedvalue(ListBox l)
{
string vtext="",vval="";
var selectedQueryText = l.Items.Cast<ListItem>().Where(item => item.Selected);
var selectedQueryVal = l.Items.Cast<ListItem>().Where(item => item.Selected).Select(item => item.Value);
vtext= String.Join("','", selectedQueryText ).TrimEnd();
vval= String.Join("','", selectedQueryVal ).TrimEnd();
return v;
}
I am a newbie to Linq. I am trying to write a linq query to get a min value from a set of records. I need to use groupby, where , select and min function in the same query but i am having issues when using group by clause. here is the query I wrote
var data =newTrips.groupby (x => x.TripPath.TripPathLink.Link.Road.Name)
.Where(x => x.TripPath.PathNumber == pathnum)
.Select(x => x.TripPath.TripPathLink.Link.Speed).Min();
I am not able to use group by and where together it keeps giving error .
My query should
Select all the values.
filter it through the where clause (pathnum).
Groupby the road Name
finally get the min value.
can some one tell me what i am doing wrong and how to achieve the desired result.
Thanks,
Pawan
It's a little tricky not knowing the relationships between the data, but I think (without trying it) that this should give you want you want -- the minimum speed per road by name. Note that it will result in a collection of anonymous objects with Name and Speed properties.
var data = newTrips.Where(x => x.TripPath.PathNumber == pathnum)
.Select(x => x.TripPath.TripPathLink.Link)
.GroupBy(x => x.Road.Name)
.Select(g => new { Name = g.Key, Speed = g.Min(l => l.Speed) } );
Since I think you want the Trip which has the minimum speed, rather than the speed, and I'm assuming a different data structure, I'll add to tvanfosson's answer:
var pathnum = 1;
var trips = from trip in newTrips
where trip.TripPath.PathNumber == pathnum
group trip by trip.TripPath.TripPathLink.Link.Road.Name into g
let minSpeed = g.Min(t => t.TripPath.TripPathLink.Link.Speed)
select new {
Name = g.Key,
Trip = g.Single(t => t.TripPath.TripPathLink.Link.Speed == minSpeed) };
foreach (var t in trips)
{
Console.WriteLine("Name = {0}, TripId = {1}", t.Name, t.Trip.TripId);
}
I want to convert this LINQ code
var x = from nm in names
select MyClass.SomeMethod(nm).TrimStart(',');
foreach (var vv in x)
{
// I want to group and count different types of vv here
}
to use shorter syntax, one where they do x => x in LINQ. I also want to group and count 'vv' (there could be number of similar vv's)
Well, the "dot notation" or "fluent notation" for the above is:
var x = names.Select(nm => MyClass.SomeMethod(nm).TrimStart(','));
For grouping:
var x = names.Select(nm => MyClass.SomeMethod(nm).TrimStart(','));
.GroupBy(vv => vv,
(key, group) => new { Key = key, Count = group.Count() });
Something like this?
MyClass.SomeMethod(names).TrimStart(',')
.GroupBy(x => x.vv)
.ToList()
.ForEach(x => Console.WriteLine(x.Key + ": " + x.Count()));