Try 

    var it = GetTheNestedCase();
    return it.SelectMany(x =&gt; x);

SelectMany is a LINQ transformation which essentially says &quot;For Each Item in a collection return the elements of a collection&quot;.  It will turn one element into many (hence SelectMany).  It&#39;s great for breaking down collections of collections into a flat list.  

    var lists = GetTheNestedCase();
    return
        from list in lists
        from element in list
        select element;

is another way of doing this using C# 3.0 query expression syntax.

I am using python 2.6 on XP. I have just installed py2exe, and I can successfully create a simple hello.exe from a hello.py. However, when I try using py2exe on my real program, py2exe produces a few information messages but fails to generate anything in the dist folder.  

My setup.py looks like this:

&lt;!-- language: python --&gt;

    from distutils.core import setup
    import py2exe

    setup(console=[&#39;ServerManager.py&#39;])

and the py2exe output looks like this:

&lt;!-- language: lang-none --&gt;

    python setup.py py2exe
    running py2exe
    creating C:\DevSource\Scripts\ServerManager\build
    creating C:\DevSource\Scripts\ServerManager\build\bdist.win32
       ...
       ...
    creating C:\DevSource\Scripts\ServerManager\dist
    *** searching for required modules ***
    *** parsing results ***
    creating python loader for extension &#39;wx._misc_&#39; (C:\Python26\lib\site-packages\wx-2.8-msw-unicode\wx\_misc_.pyd -&gt; wx._misc_.pyd)
    creating python loader for extension &#39;lxml.etree&#39; (C:\Python26\lib\site-packages\lxml\etree.pyd -&gt; lxml.etree.pyd)
       ...
       ...
    creating python loader for extension &#39;bz2&#39; (C:\Python26\DLLs\bz2.pyd -&gt; bz2.pyd)
    *** finding dlls needed ***

py2exe seems to have found all my imports (though I was a bit surprised to see win32 mentioned, as I am not explicitly importing it). Also, my program starts up quite happily with this command:

&lt;!-- language: lang-none --&gt;

    python ServerManager.py

Clearly I am doing something fundamentally wrong, but in the absence of any error messages from py2exe I have no idea what.


py2exe fails to generate an executable

We&#39;re writing a records management product for schools and one of the requirements is the ability to manage course schedules. I haven&#39;t looked at the code for how we deal with this (I&#39;m on a different project at the moment), but nonetheless I started wondering how best to handle one particular part of this requirement, namely how to handle the fact that each course can be held one or more days of the week, and how best to store this information in the database. To provide some context, a bare-bones `Course` table might contain the following columns:

    Course          Example Data
    ------          ------------
    
    DeptPrefix      ;MATH, ENG, CS, ...
    Number          ;101, 300, 450, ...
    Title           ;Algebra, Shakespeare, Advanced Data Structures, ...
    Description     ;...
    DaysOfWeek      ;Monday, Tuesday-Thursday, ...
    StartTime       
    EndTime           

What I&#39;m wondering is, what is the best way to handle the `DaysOfWeek` column in this (contrived) example? The problem I&#39;m having with it is that is a multi-valued field: that is, you can have a course on any day of the week, and the same course can take be held on more than one day. I know certain databases natively support multi-value columns, but is there a &quot;best practice&quot; to handle this assuming the database doesn&#39;t natively support it?

I&#39;ve come up with the following possible solutions so far, but I&#39;m wondering if anyone has anything better:

&lt;h3&gt;Possible Solution #1: Treat DaysOfWeek as a bit field&lt;/h3&gt;

This was the first thing that popped into my head (I&#39;m not sure if that&#39;s a good thing or not...). In this solution, `DaysOfWeek` would be defined as a byte, and the first 7 bits would be used to represent the days of week (one bit for each day). A 1 bit would indicate that a class was held on corresponding day of the week.

**Pros**: Easy to implement (the application can deal with the bit manipulations), works with any database.

**Cons**: Harder to write queries that use the `DaysOfWeek` column (although you could deal with this at the application level, or create views and stored procedues in the database to simplify this), breaks relational database model.

&lt;h3&gt;Possible Solution #2: Store DaysOfWeek as a string of characters&lt;/h3&gt;

This is essentially the same approach as using a bit field, but instead of dealing with raw bits, you assign a unique letter to each day of the week, and the `DaysOfWeek` column just stores a sequence of letters indicating what days a course is held on. For example, you might associate each weekday with a single-character code as follows:

    Weekday      Letter
    -------      ------
    
    Sunday       S
    Monday       M
    Tuesday      T
    Wednesday    W
    Thursday     R
    Friday       F
    Saturday     U

In this case, a course held on Monday, Tuesday, and Friday would have have the value `&#39;MTF&#39;` for `DaysOfWeek`, while a class held only on Wednesdays would have a `DaysOfWeek` value of `&#39;W&#39;`.

**Pros**: Easier to deal with in queries (i.e. You could use `INSTR`, or its equivalent, to determine if a class is held on a given day). Works with any database that supports INSTR or an equivalent function (most, I would guess...). Also friendlier to look at, and easy to see at a glance what is happening in queries that use the `DaysOfWeek` column.

**Cons**: The only real &quot;con&quot; is that, like the bitfield approach, this breaks the relational model by storing a variable number of values in a single field.

&lt;h3&gt;Possible Solution #3: Use a Lookup Table (ugly)&lt;/h3&gt;

Another possibility would be to create a new table that stores all the unique combinations of days of the week, and have the `Course.DaysOfWeek` column simply be a foreign key into this lookup table. However, this solution seems like the most inelegant one, and I only considered it because it seemed like the The Relational Way&lt;sup&gt;TM&lt;/sup&gt; to do things.

**Pros**: It&#39;s the only solution that is &quot;pure&quot; from a relational database point of view.

**Cons**: It&#39;s inelegant and cumbersome. For example, how would you design the user interface for assigning corresponding weekdays to a given course around the lookup table? I doubt a user wants to deal with choices alongs the lines of &quot;Sunday&quot;, &quot;Sunday, Monday&quot;, &quot;Sunday, Monday, Tuesday&quot;, &quot;Sunday, Monday, Tuesday, Wednesday&quot;, and so on...

&lt;h3&gt;Other Ideas?&lt;/h3&gt;

So, is there a more elegant way to handle multiple values in a single column? Or would one the proposed solutions suffice? For what it&#39;s worth, I think my second solution is probably the best of the three possible solutions that I outlined here, but I&#39;d be curious to see if someone has a different opinion (or indeed a different approach altogether).


What&#39;s the best way to store the days of the week an event takes place on in a relational database?

I would like to be able to fusion an `IEnumerable&lt;IEnumerable&lt;T&gt;&gt;` into `IEnumerable&lt;T&gt;` (i.e. merge all individual collections into one). The `Union` operators only applies to two collections. Any idea?

How to merge a collection of collections in Linq

<p>I would like to be able to fusion an <code>IEnumerable&#x3C;IEnumerable&#x3C;T>></code> into <code>IEnumerable&#x3C;T></code> (i.e. merge all individual collections into one). The <code>Union</code> operators only applies to two collections. Any idea?</p>


Edit:

Of course my real code doesn&#39;t look exactly like this. I tried to write semi-pseudo code to make it more clear of whay I wanted to do.

Looks like it just messed things up instead.

So, what I actually would like to do is this:

    Method&lt;Interface1&gt;();
    Method&lt;Interface2&gt;();
    Method&lt;Interface3&gt;();
    ...

Well ... I thought that maybe I could turn it into a loop using reflection. So the question is: How how do I do it. I have _very_ shallow knowledge of reflection. So code examples would be great.

The scenario looks like this:

    public void Method&lt;T&gt;() where T : class
    {}
    public void AnotherMethod()
    {
        Assembly assembly = Assembly.GetExecutingAssembly();
    
        var interfaces = from i in assembly.GetTypes()
        where i.Namespace == &quot;MyNamespace.Interface&quot; // only interfaces stored here
        select i;
    
        foreach(var i in interfaces)
        {
            Method&lt;i&gt;(); // Get compile error here!
        }

&lt;br&gt;&lt;br&gt;


----------


Original post:

Hi!

I&#39;m trying to loop through all interfaces in a namespace and send them as arguments to a generic method like this:

    public void Method&lt;T&gt;() where T : class
    {}
    public void AnotherMethod()
    {
        Assembly assembly = Assembly.GetExecutingAssembly();
    
        var interfaces = from i in assembly.GetTypes()
        where i.Namespace == &quot;MyNamespace.Interface&quot; // only interfaces stored here
        select i;
    
        foreach(var interface in interfaces)
        {
            Method&lt;interface&gt;(); // Get compile error here!
        }
    }
The error I get is &quot;Type name expected, but local variable name found&quot;.
If I try

    ...
        foreach(var interface in interfaces)
        {
            Method&lt;interface.MakeGenericType()&gt;(); // Still get compile error here!
        }
    }

I get &quot;Cannot apply operator &#39;&lt;&#39; to operands of type &#39;method group&#39; and &#39;System.Type&#39;&quot;
Any idea on how to get around this problem?
&lt;/em&gt;





Calling generic method with a type argument known only at execution time

I want to test my Entities that are built using Entity Framework.
My concern is that using Entity Framework means directly working with data source.
So any ideas how to unit testing Entity Framework based components?

Unit testing with Entity Framework

Any idea on how to check whether that list is a subset of another?

Specifically, I have

    List&lt;double&gt; t1 = new List&lt;double&gt; { 1, 3, 5 };
    List&lt;double&gt; t2 = new List&lt;double&gt; { 1, 5 };

How to check that t2 is a subset of t1, using LINQ?

Check whether an array is a subset of another

What is the best way to get the Max value from a LINQ query that may return no rows? If I just do

    Dim x = (From y In context.MyTable _
             Where y.MyField = value _
             Select y.MyCounter).Max

I get an error when the query returns no rows. I could do

    Dim x = (From y In context.MyTable _
             Where y.MyField = value _
             Select y.MyCounter _
             Order By MyCounter Descending).FirstOrDefault

but that feels a little obtuse for such a simple request. Am I missing a better way to do it?

UPDATE: Here&#39;s the back story: I&#39;m trying to retrieve the next eligibility counter from a child table (legacy system, don&#39;t get me started...). The first eligibility row for each patient is always 1, the second is 2, etc. (obviously this is not the primary key of the child table). So, I&#39;m selecting the max existing counter value for a patient, and then adding 1 to it to create a new row. When there are no existing child values, I need the query to return 0 (so adding 1 will give me a counter value of 1). Note that I don&#39;t want to rely on the raw count of child rows, in case the legacy app introduces gaps in the counter values (possible). My bad for trying to make the question too generic.

Max or Default?

I need to do a LINQ2DataSet query that does a join on more than one field (as

    var result = from x in entity
    join y in entity2 
           on x.field1 = y.field1 
    and 
              x.field2 = y.field2

I have yet found a suitable solution (I can add the extra constraints to a where clause, but this is far from a suitable solution, or use [this][1] solution, but that assumes an equijoin).

Is it possible in LINQ to join on multiple fields in a single join?

**EDIT**

    var result = from x in entity
                 join y in entity2
                 on new { x.field1, x.field2 } equals new { y.field1, y.field2 }

is the solution I referenced as assuming an equijoin above.

Further **EDIT**

To answer criticism that my original example was an equijoin, I do acknowledge that, My current requirement is for an equijoin and I have already employed the solution I referenced above.

I am, however, trying to understand what possibilities and best practices I have / should employ with LINQ. I am going to need to do a Date range query join with a table ID soon, and was just pre-empting that issue, It looks like I shall have to add the date range in the where clause.

Thanks, as always, for all suggestions and comments given

  [1]: https://stackoverflow.com/questions/345427/linq-to-sql-join-multiple-columns-from-the-same-table

How to do joins in LINQ on multiple fields in single join

I&#39;ve always been one to simply use:

    List&lt;String&gt; names = new ArrayList&lt;&gt;();

I use the interface as the type name for _portability_, so that when I ask questions such as this, I can rework my code.  
  
When should [`LinkedList`][1] be used over [`ArrayList`][2] and vice-versa?


  [1]: https://docs.oracle.com/javase/9/docs/api/java/util/LinkedList.html
  [2]: https://docs.oracle.com/javase/9/docs/api/java/util/ArrayList.html

When to use LinkedList over ArrayList in Java?

When I have entities in my domain with lists of things, should they be exposed as ILists or IEnumerables? E.g. Order has a bunch of OrderLines. 

IList vs IEnumerable for Collections on Entities

I&#39;ve seen them used in a lot of the same ways, and I am worried I&#39;m about to go down a path in design that is irreversible if I don&#39;t understand this better. Also, I am using .NET.

What is the difference between List (of T) and Collection(of T)?

I&#39;m a beginner in Java.  Please suggest which collection(s) can/should be used for maintaining a sorted list in Java. I have tried `Map` and `Set`, but they weren&#39;t what I was looking for.


Sorted collection in Java

What is the best way to convert a JSON code as this:

    { 
        &quot;data&quot; : 
        { 
            &quot;field1&quot; : &quot;value1&quot;, 
            &quot;field2&quot; : &quot;value2&quot;
        }
    }

in a Java Map in which one the keys are (field1, field2) and the values for those fields are (value1, value2).

Any ideas? Should I use Json-lib for that? Or better if I write my own parser?




Convert JSON to Map

I have the name of the &quot;sort by property&quot; in a string. I will need to use Lambda/Linq to sort the list of objects.

Ex:

    public class Employee
    {
      public string FirstName {set; get;}
      public string LastName {set; get;}
      public DateTime DOB {set; get;}
    }
    
    
    public void Sort(ref List&lt;Employee&gt; list, string sortBy, string sortDirection)
    {
      //Example data:
      //sortBy = &quot;FirstName&quot;
      //sortDirection = &quot;ASC&quot; or &quot;DESC&quot;

      if (sortBy == &quot;FirstName&quot;)
      {
        list = list.OrderBy(x =&gt; x.FirstName).toList();    
      }
    
    }

1. Instead of using a bunch of ifs to check the fieldname (sortBy), is there a cleaner way of doing the sorting
2. Is sort aware of datatype?

Sorting a list using Lambda/Linq to objects

Is there a way in Linq to do an OrderBy against a set of values (strings in this case) without knowing the order of the values?

Consider this data:

    A
    B
    A
    C
    B
    C
    D
    E

And these variables:

string firstPref, secondPref, thirdPref;

When the values are set like so:

    firstPref = &#39;A&#39;;
    secondPref = &#39;B&#39;;
    thirdPref = &#39;C&#39;;

Is it possible to order the data like so:

    A
    A
    B
    B
    C
    C
    D
    E

Linq OrderBy against specific values

Using the C# compilers query comprehension features, you can write code like:

    var names = new string[] { &quot;Dog&quot;, &quot;Cat&quot;, &quot;Giraffe&quot;, &quot;Monkey&quot;, &quot;Tortoise&quot; };
    var result =
        from animalName in names
        let nameLength = animalName.Length
        where nameLength &gt; 3
        orderby nameLength
        select animalName; 

In the query expression above, the `let` keyword allows a value to be passed forward to the where and orderby operations without duplicate calls to `animalName.Length`.

What is the equivalent set of LINQ extension method calls that achieves what the &quot;let&quot; keyword does here?

Code equivalent to the &#39;let&#39; keyword in chained LINQ extension method calls

I&#39;m using LINQPad to create LINQ queries in an application I&#39;m bulding.

I noticed that in the downloaded **LINQ in Action** samples, e.g. example 4.04, intellisense shows a class &quot;Books&quot; but I don&#39;t see any **references** or &quot;**using**&quot; statements in the LINQPad tool, here is the sample:

    List&lt;Book&gt; books = new List&lt;Book&gt;() {
      new Book { Title=&quot;LINQ in Action&quot; },
      new Book { Title=&quot;LINQ for Fun&quot; },
      new Book { Title=&quot;Extreme LINQ&quot; } };
    
    var titles =
      books
        .Where(book =&gt; book.Title.Contains(&quot;Action&quot;))
        .Select(book =&gt; book.Title);
    
    titles.Dump();

In &quot;LinqBooks.Common, Business Objects, **Book.linq**&quot; is where the class seems to be defined:

    public class Book
    {
      public IEnumerable&lt;Author&gt; Authors {get; set;}
      public String Isbn {get; set;}
      public String Notes {get; set;}
      public Int32 PageCount {get; set;}
      public Decimal Price {get; set;}
      public DateTime PublicationDate {get; set;}
      public Publisher Publisher {get; set;}
      public IEnumerable&lt;Review&gt; Reviews {get; set;}
      public Subject Subject {get; set;}
      public String Summary {get; set;}
      public String Title {get; set;}
      public String Test {get; set;}
    
      public override String ToString()
      {
        return Title;
      }
    }

**But how does this work so that I can copy in my classes and use LINQPad to quickly build LINQ statements that I can then copy back into my application?**


How does LINQPad reference other classes, e.g. Books in the LINQ in Action samples

Just a little niggle about LINQ syntax. I&#39;m flattening an `IEnumerable&lt;IEnumerable&lt;T&gt;&gt;` with `SelectMany(x =&gt; x)`.

My problem is with the lambda expression `x =&gt; x`. It looks a bit ugly. Is there some static &#39;identity function&#39; object that I can use instead of `x =&gt; x`? Something like `SelectMany(IdentityFunction)`?


Content Type	Original Author	Original Content on Stackoverflow
Question	Joannes Vermorel	View Question on Stackoverflow
Solution 1 - Linq	JaredPar	View Answer on Stackoverflow
Solution 2 - Linq	Joe Chung	View Answer on Stackoverflow

How to merge a collection of collections in Linq

Linq Problem Overview

Linq Solutions

Solution 1 - Linq

Solution 2 - Linq

What's the best way to store the days of the week an event takes place on in a relational database?

py2exe fails to generate an executable

Attributions