I have a list of items 'ActiveNodes'. Each item belongs to a 'tier' and so has a tierID. TierID is not unique. What I want to do is loop though all items by tier and then each item within the tier. This is how I've approached it, but given the flexibility of linq , I wondered if there was any better approach.
var tiers = ActiveNodes.Select(x => x.TierID).Distinct();
foreach (var t in tiers)
{
var nodes = ActiveNodes.Where(x => x.TierID == t);
foreach(var n in nodes)
{
// do something
}
}
You should use GroupBy:
var tiers = ActiveNodes.GroupBy(x => x.TierID);
foreach (var t in tiers)
{
// Id for current group can be taken from t.Key property
var tierId = t.Key;
// t implements IEnumerable<Node>, so you can loop over it directly
foreach(var n in t)
{
// do something
}
}
Related
I am busy with a small online voting web app, now I struggling to get the total number of votes for each party that I stored in a different table. Here is what I have tried, this method gets each party from the votes table named [dbo].[VoterCandidateMapping]
public List<int> GetAllPartIDs()
{
List<int> partieIDs = new List<int>();
var parties = (from votes in voteDB.VoterCandidateMappings
select votes.PartyID).Distinct().ToList();
partieIDs = parties;
return partieIDs;
}
Then I want to use this method to count each vote associated with a particular part, here is the code
public IQueryable<ResultsViewModel> GetResults()
{
int numberOfVotes = 0;
foreach (int IDs in GetAllPartIDs())
{
numberOfVotes = (from votes in voteDB.VoterCandidateMappings
where votes.PartyID == IDs ? true : false
select votes.VoterID).Count();
}
return (
from results in voteDB.VoterCandidateMappings
join parties in voteDB.Parties
on results.PartyID equals parties.Id
select new ResultsViewModel
{
PartyName = parties.Name,
TotalVotes = numberOfVotes
});
}
It runs and return almost every data but the total number of votes is the same
The reason why it does not work is that you are trying to store multiple values in a single numberOfVotes variable.
Let's go through code what you have now.
First foreach loop calculate votes for each party and assigns to numberOfVotes variable. Each time value is assigned, existing value in numberOfVotes is overwritten. In the end of loop numberOfVotes contains number of votes for the last party. This is value you are seeing in your results as you use the same variable to return results.
Here is one way to do it correctly:
public IQueryable<ResultsViewModel> GetResults()
{
var groupedVotes = voteDB.VoterCandidateMappings
.GroupBy(x => x.PartyID)
.Select(x => new { PartyId = x.Key, NumberOfVotes = x.Count());
return voteDB.Parties
.Select(x => new ResultsViewModel
{
PartyName = x.Name,
TotalVotes = groupedVotes
.Where(y => y.PartyId == x.Id)
.Select(y => y.NumberOfVotes)
.FirstOrDefault()
});
}
I have a problem with a query. I have a List with int and want to use it to get the values from my dictionary. The dictionary-keys are int and some of them have the value of the list-items. My question is how i get the objects out of the dictionary, thats keys matces the list items. Was programming JAVA the last years and now struggling with LINQ :(
Thanks in advance
Problem solved. Thank you all :)
No idea how to close this topic. I am reading stackoverflow since one year, but this was my first post.
You can use Linq to join list items with dictionary KeyValuePair entries on entry key. And then select entry value from each joined pair:
var values = from l in list
join kvp in dictionary on l equals kvp.Key
select kvp.Value;
Lambda syntax:
var values = list.Join(dictionary, l => l, kvp => kvp.Key, (l,kvp) => kvp.Value);
Basically:
var value = dictionary[integerKey];
Or:
if (dictionary.TryGetValue(integerKey, out value)) {
}
You can also create an extension method:
public static class DictionaryExtensions
{
public static IEnumerable<TValue> FilterValuesBy<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, IEnumerable<TKey> filter)
{
if (dictionary == null) throw new ArgumentNullException("dictionary");
if (filter == null) throw new ArgumentNullException("filter");
var coll = filter as ICollection<TKey> ?? new HashSet<TKey>(filter);
return dictionary.Where(kvp => coll.Contains(kvp.Key)).Select(kvp => kvp.Value);
}
}
Usage:
class Program
{
static void Main()
{
var dict = Enumerable.Range(0, 10).ToDictionary(x => x);
var filter = Enumerable.Range(0, 2);
foreach (var i in dict.FilterValuesBy(filter))
{
Console.WriteLine(i);
}
Console.ReadLine();
}
}
Simple Linq method chain:
var dict = Enumerable.Range(0, 10).ToDictionary(x => x);
var filter = Enumerable.Range(0, 2).ToList();
var filtered = dict.Where(x => filter.Contains(x.Key)).Select(x => x.Value).ToList();
I have a list of items in an IList<>.Each listitem has a date and a few other fields.
I need to order the list by date and then change the list to only show a date for the first item and effectively set the date field to null for the other items if the date is repeated.
Example:
12/01/2012 500
12/01/2012 700
15/02/2012 900
15/02/2012 1100
27/05/2012 2000
Desired Result:
12/01/2012 500
null 700
15/02/2012 900
null 1100
27/05/2012 2000
Is this possible with the linq group by and order by?
Thanks
LINQ operators are not supposed to change the underlying data. You'd better use regular foreach if you're going to modify the data.
This should probably work:
var groups = items.GroupBy(x => x.Date).ToArray();
foreach (var group in groups)
{
foreach (var item in group.Skip(1)) item.Date = null;
}
I would avoid using such a construction since you'll have to double-check that GroupBy preserves order. Instead I would use something like this:
var sortedItems = items.OrderBy(x => x.Date);
var lastVisitedDate = (DateTime?) null;
foreach (var item in sortedItems)
if (Equals(item.Date, lastVisitedDate)) item.Date = null;
else lastVisitedDate = item.Date;
This should work:
var list = new List<DateItem>();
// Initialization ...
var dups = list.Select((Item,Index) => new{ Item,Index })
.GroupBy(x => x.Item.Date)
.Where(g => g.Count() > 1);
foreach(var dup in dups)
{
foreach (var nullable in dup.OrderBy(x => x.Item.Date).Skip(1))
{
list[nullable.Index].Date = null;
}
}
Assuming your class looks similar to this:
class DateItem {
public DateTime? Date;
public int OtherField;
}
Edit: Here's a working demo: http://ideone.com/cVL4G
One way is to use LINQ to get all of the followers and then set their dates to null in a loop:
// Use ToList() to make sortedItems non-lazy so it won't get ordered each time it's called.
var sortedItems = items.OrderBy(x => x.Date).ToList();
var followers = sortedItems.GroupBy(item => item.Date)
.SelectMany(group => group.Skip(1));
foreach (var follower in followers)
{
follower.Date = null;
}
// Now you can use sortedItems.
Or if you prefer the query syntax:
var followers = from item in sortedItems
group item by item.Date into grp
from follower in grp.Skip(1)
select follower;
I have 3 tables, team(id,name) player(id,teamid,name) playerdetail(id,playerid,height,weight), the relationship between team and player is one to many, the relationship between player and playerdetail is one to one.
I want to use eager loading to load all the information and print out the name of players who is higher than 2 meters.
I have write the code below,
using (var context = new TestEntities())
{
var query = from t in context.Teams.Include("Players.PlayerDetails") select t;
foreach (var v in query)
{
Console.WriteLine(v.Players.Any(x => x.PlayerDetails.Any(y => y.Height > 200)));
}
Console.Read();
}
It prints out only true and false, how can I modify it and make it print out the name of player?
Thanks in advance
Why don't you just query the players through context.Players like below?
using (var context = new TestEntities())
{
var query = context.Players.Include("Team").Include("PlayerDetails")
.Where(p => p.Height > 200);
foreach (var v in query)
{
Console.WriteLine(v.Name);
}
Console.Read();
}
I have an array-list that contains some UserID.
I need a query like this:
vat tmp= users.select(a=> a.UserID in (arraylist));
what can I do?
If it's actually in an ArrayList, you should create a List<T> or array first. Then you can use Contains:
// Use the appropriate type, of course.
var ids = arraylist.Cast<string>().ToList();
var tmp = users.Select(a => ids.Contains(a.UserID));
While using Contains on the plain ArrayList may well compile, I would expect it to fail at execution time, assuming users is an IQueryable<>.
List<long> list =new List<long>();
var selected = from n in users where list.Contains(n.ID) select n ;
OR
var selected = users.Where(a=> list.Contains(a.ID)).ToList();
This is the solution I used.
public static IEnumerable<SettingModel> GetSettingBySettingKeys(params string[] settingKey)
{
using (var db = new BoxCoreModelEntities())
{
foreach (var key in settingKey)
{
var key1 = key;
yield return Map(db.Settings.Where(s => s.SettingKey == key1).First());
}
}
}