I need your help for a small problem. I would like to make the following LINQ query dynamic (at runtime) because I don´t know how many tables there will be in the database (the tablenames are known while runtime).
var query = from row1 in ds.Tables["tab1"].AsEnumerable()
from row2 in ds.Tables["tab2"].AsEnumerable()
from row3 in ds.Tables["tab3"].AsEnumerable()
select new { row1, row2, row3 };
Is this possible at generate a dynamic LINQ query in this case and write the result to a datatable or array?
Thanks in advance!
This extension method can create a cartesian product of all tables rows in a DataSet.
public static class Extensions
{
public static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
{
IEnumerable<IEnumerable<T>> emptyProduct = new[] { Enumerable.Empty<T>() };
return sequences.Aggregate(
emptyProduct,
(accumulator, sequence) =>
from accseq in accumulator
from item in sequence
select accseq.Concat(new[] { item })
);
}
}
Now you can use it in this way:
IEnumerable<IEnumerable<DataRow>> allTablesRows = ds.Tables.Cast<DataTable>()
.Select(table => table.AsEnumerable())
.CartesianProduct();
Output:
foreach (var x in allTablesRows)
{
foreach (DataRow row in x)
{
Console.WriteLine("table:{0} fields:{1}",
row.Table.TableName,
string.Join(",", row.ItemArray));
}
}
Related
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 array of string say:
String[] Fields=new String[]{RowField,RowField1}
In which I can use the below query to get the values by specifying the values is query i.e RowField and RowField1:
var Result = (
from x in _dataTable.AsEnumerable()
select new
{
Name = x.Field<object>(RowField),
Name1 = x.Field<object>(RowField1)
})
.Distinct();
But if suppose I have many values in the Array like:
String[] Fields= new String[]
{
RowField,
RowField1,
RowField2,
.......
RowField1000
};
How can I use the query here without specifying each of the rowfield in the query?
How can i iterate through the array items inside the LINQ?
According to some suggestions in LINQ query and Array of string I am trying to get the result using the code below.
var result = (from row in _dataTable.AsEnumerable()
let projection = from fieldName in fields
select new {Name = fieldName, Value = row[fieldName]}
select projection.ToDictionary(p=>p.Name,p=>p.Value))
.Distinct();
But the problem is it does not return the distinct values.Any ideas?
Start with distinct DataRows by using this overload of Distinct():
_dataTable.AsEnumerable().Distinct(new DataRowEqualityComparer())
Where DataRowEqualityComparer is:
public class DataRowEqualityComparer : IEqualityComparer<DataRow>
{
public bool Equals(DataRow x, DataRow y)
{
return x.ItemArray.SequenceEqual(y.ItemArray);
}
public int GetHashCode(DataRow obj)
{
return string.Join("", obj.ItemArray).GetHashCode();
}
}
I have a dataset table, I want to group it by column MOID, and then within this group I want to select the row which has max value of column radi.
Can anybody show me how to do it via LINQ to dataset?
Although the solution posted by Barry should work (with a few fixes), it is sub-optimal : you don't need to sort a collection to find the item with the maximum value of a field. I wrote a WithMax extension method, which returns the item with the maximum value of the specified function :
public static T WithMax<T, TValue>(this IEnumerable<T> source, Func<T, TValue> selector)
{
var max = default(TValue);
var withMax = default(T);
bool first = true;
var comparer = Comparer<TValue>.Default;
foreach (var item in source)
{
var value = selector(item);
int compare = comparer.Compare(value, max);
if (compare > 0 || first)
{
max = value;
withMax = item;
}
first = false;
}
return withMax;
}
It iterates the collection only once, which is much faster than sorting it just to get the first item.
You can then use it as follows
var query =
from row in table.AsEnumerable()
group row by row.Field<int>("MOID") into g
select g.WithMax(r => r.Field<int>("radi"));
This is untested but I think something like this should work:
var qry = from m in [YourDataSource]
group p by m.MOID into grp
select grp.OrderByDescending(a => a.RADI).First();
this works with one query!
public static T WithMax<T, TValue>(this IEnumerable<T> source, Func<T, TValue> keySelector)
{
return source.OrderByDescending(keySelector).FirstOrDefault();
}
I am using SubSonic 3.0.0.3 along with the Linq T4 Templates. My ProjectRepository, for example, has the following two methods:
public int Add(Project item)
{
int result = 0;
ISqlQuery query = BuildInsertQuery(item);
if (query != null)
{
result = query.Execute();
}
return result;
}
private ISqlQuery BuildInsertQuery(Project item)
{
ITable tbl = FindTableByClassName();
Insert query = null;
if (tbl != null)
{
Dictionary<string, object> hashed = item.ToDictionary();
query = new Insert(_db.Provider).Into<Project>(tbl);
foreach (string key in hashed.Keys)
{
IColumn col = tbl.GetColumn(key);
if (col != null)
{
if (!col.AutoIncrement)
{
query.Value(key, hashed[key]);
}
}
}
}
return query;
}
Along with performing the insert (which works great), I'd really like to get the value of the auto-incrementing ProjectId column. For the record, this column is both the primary key and identity column. Is there perhaps a way to append "SELECT SCOPE_IDENTITY();" to the query or maybe there's an entirely different approach which I should try?
You can do this with the ActiveRecord templates which does all of the wiring above for you (and also has built-in testing). In your scenario, the Add method would have one line: Project.Add() and it would return the new id.
For your needs, you can try this:
var cmd=query.GetCommand();
cmd.CommandSql+=";SELECT SCOPE_IDENTITY() as newid";
var newID=query.Provider.ExecuteScalar(cmd);
That should work..
*Edit - you can create an ExtensionMethod for this on ISqlQuery too, to save some writing...
I have got a collection. The coll has strings:
Location="Theater=1, Name=regal, Area=Area1"
Location="Theater=34, Name=Karm, Area=Area4445"
and so on. I have to extract just the Name bit from the string. For example, here I have to extract the text 'regal' and group the query. Then display the result as
Name=regal Count 33
Name=Karm Count 22
I am struggling with the query:
Collection.Location.GroupBy(????);(what to add here)
Which is the most short and precise way to do it?
Yet another Linq + Regex approach:
string[] Location = {
"Theater=2, Name=regal, Area=Area1",
"Theater=2, Name=regal, Area=Area1",
"Theater=34, Name=Karm, Area=Area4445"
};
var test = Location.Select(
x => Regex.Match(x, "^.*Name=(.*),.*$")
.Groups[1].Value)
.GroupBy(x => x)
.Select(x=> new {Name = x.Key, Count = x.Count()});
Query result for tested strings
Once you've extracted the string, just group by it and count the results:
var query = from location in locations
let name = ExtractNameFromLocation(location)
group 1 by name in grouped
select new { Name=grouped.Key, Count=grouped.Count() };
That's not particularly efficient, however. It has to do all the grouping before it does any counting. Have a look at this VJ article for an extension method for LINQ to Objects,
and this one about Push LINQ which a somewhat different way of looking at LINQ.
EDIT: ExtractNameFromLocation would be the code taken from answers to your other question, e.g.
public static string ExtractNameFromLocation(string location)
{
var name = (from part in location.Split(',')
let pair = part.Split('=')
where pair[0].Trim() == "Name"
select pair[1].Trim()).FirstOrDefault();
return name;
}
Here is another LINQ alternative solution with a working example.
static void Main(string[] args)
{
System.Collections.Generic.List<string> l = new List<string>();
l.Add("Theater=1, Name=regal, Area=Area"); l.Add("Theater=34, Name=Karm, Area=Area4445");
foreach (IGrouping<string, string> g in l.GroupBy(r => extractName(r)))
{
Console.WriteLine( string.Format("Name= {0} Count {1}", g.Key, g.Count()) );
}
}
private static string extractName(string dirty)
{
System.Text.RegularExpressions.Match m =
System.Text.RegularExpressions.Regex.Match(
dirty, #"(?<=Name=)[a-zA-Z0-9_ ]+(?=,)");
return m.Success ? m.Value : "";
}