From the documentation for [Skip](http://msdn.microsoft.com/en-us/library/bb358985.aspx):

&gt; Bypasses a specified number of elements in a sequence and then returns the remaining elements.

So you just need this:

    foreach (var item in list.Skip(1))

Just do:

    foreach (var item in input.Skip(1))

There&#39;s some more info on the [MSDN][1] and a simple example that&#39;s downloadable [here][2]

 [1]: http://msdn.microsoft.com/en-us/library/bb386988.aspx
 [2]: http://msdn.microsoft.com/en-us/vcsharp/aa336757.aspx#SkipSimple

Wouldn&#39;t it be...

    foreach (var in list.Skip(1).AsEnumerable())



I&#39;m looking for help using sum() in my SQL query:

    SELECT links.id, 
           count(DISTINCT stats.id) as clicks, 
           count(DISTINCT conversions.id) as conversions, 
           sum(conversions.value) as conversion_value 
    FROM links 
    LEFT OUTER JOIN stats ON links.id = stats.parent_id 
    LEFT OUTER JOIN conversions ON links.id = conversions.link_id 
    GROUP BY links.id 
    ORDER BY links.created desc;

I use `DISTINCT` because I&#39;m doing &quot;group by&quot; and this ensures the same row is not counted more than once.

The problem is that SUM(conversions.value) counts the &quot;value&quot; for each row more than once (due to the group by)

I basically want to do `SUM(conversions.value)` for each DISTINCT conversions.id.

Is that possible?

MYSQL sum() for distinct rows

I have developed a simple location aware iPhone application which is functionally working very well to our expectations except in the low memory condition of the phone .

In low memory condition of the phone my app just crashes and If I increases the phone memory by freeing up some space it again start working well without any crash .

when I did some googling on the problem I found that in the low memory conditions the OS will send didReceiveMemoryWarning to all the controllers in the current hierarchy so that each one of them should implement didReceiveMemoryWarning method and also set iboutlet to nil for the view that is currently not visible . 

I have also read somewhere that if the view for that controller is not visible the method **setView** with nil parameter will be called and if there are some outlet variables attached to view there will be problem in removing them.


So with all these fundas what is the best to handle low level memory condition raised by the Iphone by implementing the  **didReceiveMemoryWarning** and **viewDidUnload** methods.

Please give a proper example or link if possible for the solution of the above problem .

thanks.

How to implement didReceiveMemoryWarning?

i would like to iterate over the items of a `List&lt;T&gt;`, except the first, preserving the order. Is there an elegant way to do it with LINQ using a statement like:

&gt;foreach (var item in list.Skip(1).**TakeTheRest()**)
&gt;{....

I played around with `TakeWhile` , but was not successful. Probably there is also another, simple way of doing it?

LINQ: How to skip one then take the rest of a sequence

i would like to iterate over the items of a <code>List&#x3C;T></code>, except the first, preserving the order. Is there an elegant way to do it with LINQ using a statement like:
>foreach (var item in list.Skip(1).TakeTheRest())
>{....
I played around with <code>TakeWhile</code> , but was not successful. Probably there is also another, simple way of doing it?

let&#39;s say that I have a table called
Items (ID int, Done int, Total int)

I can do it by two queries:

    int total = m.Items.Sum(p=&gt;p.Total)
    int done = m.Items.Sum(p=&gt;p.Done)

But I&#39;d like to do it in one query, something like this:

    var x = from p in m.Items select new { Sum(p.Total), Sum(p.Done)};
Surely there is a way to call aggregate functions from LINQ syntax...? 


Get sum of two columns in one LINQ query

Googling is only coming up with the keyword, but I stumbled across some code that says 

    MyVariable = default(MyObject);

and I am wondering what it means.

What does default(object); do in C#?

I would like to test an app that uses the Clipboard (WindowsForms) and I need the Clipboard in my unit tests also.  In order to use it, it should run in STA mode, but since the NUnit `TestFixture` does not have a main method, I don&#39;t know where/how to annotate it.


How to run unit tests in STAThread mode?

I have the following method to save an Object to a file:

    // Save an object out to the disk
    public static void SerializeObject&lt;T&gt;(this T toSerialize, String filename)
    {
        XmlSerializer xmlSerializer = new XmlSerializer(toSerialize.GetType());
        TextWriter textWriter = new StreamWriter(filename);

        xmlSerializer.Serialize(textWriter, toSerialize);
        textWriter.Close();
    }

I confess I did not write it (I only converted it to a extension method that took a type parameter).

Now I need it to give the xml back to me as a string (rather than save it to a file).  I am looking into it, but I have not figured it out yet.

I thought this might be really easy for someone familiar with these objects.  If not I will figure it out eventually.

Serialize an object to string

I follow this rule but some of my colleagues disagree with it and argue that if a class is smaller it can be left in the same file with other class(es).

Another argument I hear all the time is &quot;Even Microsoft doesn&#39;t do this, so why should we?&quot;

What&#39;s the general consensus on this? Are there cases where this should be avoided?

One class per file rule in .NET?

I&#39;m confused as to the difference.  Being fairly new to .Net, I know I can query `IEnumerables` using the Linq extensions.  So what is this `IQueryable` and how does it differ?

------------
See also [What is the difference between IQueryable[T] and IEnumerable[T]?][1] that overlaps with this question.


  [1]: https://stackoverflow.com/questions/252785/what-is-the-difference-between-iqueryablet-and-ienumerablet/25664959

What&#39;s the difference between IQueryable and IEnumerable

I&#39;ve been working for quite a while now with LINQ. However, it remains a bit of a mystery what the real differences are between the mentioned flavours of LINQ. 

**The successful answer will contain a short differentiation between them. What is the main goal of each flavor, what is the benefit, and is there a performance impact...**

P.S.
I know that there are a lot of information sources out there, but I&#39;m looking for a kind of a &quot;cheat sheet&quot; which instructs a newbie where to head for a specific goal.

What is the difference between &quot;LINQ to Entities&quot;, &quot;LINQ to SQL&quot; and &quot;LINQ to Dataset&quot;

Given a datasource like that:

    var c = new Car[]
    {
      new Car{ Color=&quot;Blue&quot;, Price=28000},
      new Car{ Color=&quot;Red&quot;, Price=54000},
      new Car{ Color=&quot;Pink&quot;, Price=9999},
      // ..
    };

How can I find the **index** of the first car satisfying a certain condition with LINQ?

EDIT:

I could think of something like this but it looks horrible:

    int firstItem = someItems.Select((item, index) =&gt; new    
    {    
        ItemName = item.Color,    
        Position = index    
    }).Where(i =&gt; i.ItemName == &quot;purple&quot;)    
      .First()    
      .Position;

Will it be the best to solve this with a plain old loop?


How to get index using LINQ?

I have an `List&lt;int&gt;` which contains 1,2,4,7,9 for example.

I have a range from 0 to 10.

Is there a way to determine what numbers are missing in that sequence?

I thought LINQ might provide an option but I can&#39;t see one

In the real world my List could contain 100,000 items so performance is key

Check for missing number in sequence

If I have some R list `mylist`, you can append an item `obj` to it like so:

    mylist[[length(mylist)+1]] &lt;- obj

But surely there is some more compact way.  When I was new at R, I  tried writing `lappend()` like so:

    lappend &lt;- function(lst, obj) {
        lst[[length(lst)+1]] &lt;- obj
        return(lst)
    }

but of course that doesn&#39;t work due to R&#39;s call-by-name semantics (`lst` is effectively copied upon call, so changes to `lst` are not visible outside the scope of `lappend()`.  I know you can do environment hacking in an R function to reach outside the scope of your function and mutate the calling environment, but that seems like a large hammer to write a simple append function.

Can anyone suggest a more beautiful way of doing this? Bonus points if it works for both vectors and lists.

Append an object to a list in R in amortized constant time, O(1)?

I want to write a function that reads a list `[1,5,3,6,...]`
and gives `[1,1,5,5,3,3,6,6,...]`.
Any idea how to do it?


Duplicate each member in a list

I have a big file I&#39;m reading from, and convert every few lines to an instance of an Object.

Since I&#39;m looping through the file, I stash the instance to a list using list.append(instance), and then continue looping.

This is a file that&#39;s around ~100MB so it isn&#39;t too large,  but as the list grows larger, the looping slows down progressively.  (I print the time for each lap in the loop).


This is not intrinsic to the loop ~ when I print every new instance as I loop through the file, the program progresses at constant speed ~ it is only when I append them to a list it gets slow.

My friend suggested disabling garbage collection before the while loop and enabling it afterward &amp; making a garbage collection call.

Did anyone else observe a similar problem with list.append getting slower?  Is there any other way to circumvent this?

----------

I&#39;ll try the following two things suggested below.

(1) &quot;pre-allocating&quot; the memory ~ what&#39;s the best way to do this? (2) Try using deque

Multiple posts (see comment by Alex Martelli) suggested memory fragmentation (he has a large amount of available memory like I do)  ~ but no obvious fixes to performance for this.

To replicate the phenomenon, please run the test code provided below in the answers and assume that the lists have useful data.

----------

gc.disable() and gc.enable() helps with the timing. I&#39;ll also do a careful analysis of where all the time is spent.


Is there a way to circumvent Python list.append() becoming progressively slower in a loop as the list grows?

I&#39;m using Python&#39;s `max` and `min` functions on lists for a minimax algorithm, and I need the index of the value returned by `max()` or `min()`. In other words, I need to know which move produced the max (at a first player&#39;s turn) or min (second player) value.

    for i in range(9):
        new_board = current_board.new_board_with_move([i / 3, i % 3], player)
    
        if new_board:
            temp = min_max(new_board, depth + 1, not is_min_level)  
            values.append(temp)

    if is_min_level:
        return min(values)
    else:
        return max(values)

I need to be able to return the actual index of the min or max value, not just the value.

Getting the index of the returned max or min item using max()/min() on a list

I&#39;m looking for an equivalent in python of `dictionary.get(key, default)` for lists. Is there any one liner idiom to get the nth element of a list or a default value if not available?

For example, given a list myList I would like to get `myList[0]`, or 5 if`myList` is an empty list.

Thanks.

How to get the nth element of a python list or a default if not available

So I want to iterate for each character in a string.

So I thought:

    for (char c : &quot;xyz&quot;)

but I get a compiler error:

    MyClass.java:20: foreach not applicable to expression type

How can I do this?

How do I apply the for-each loop to every character in a String?

If I wanted to do something like this:

    collection.each do |i|
       return nil if i == 3
    
       ..many lines of code here..
    end

How would I get that effect? I know I could just wrap everything inside the block in a big if statement, but I&#39;d like to avoid the nesting if possible.

Break would not work here, because I do *not* want to stop iteration of the remaining elements.

How can I return something early from a block?

I need to execute a command 100-200 times, and so far my research indicates that I would either have to copy/paste 100 copies of this command, OR use a `for` loop, but the `for` loop expects a list of items, hence I would need 200 files to operate on, or a list of 200 items, defeating the point.

I would rather not have to write a C program and go through the length of documenting why I had to write another program to execute my program for test purposes. Modification of my program itself is also not an option.

**So, given a command, `a`, how would I execute it `N` times via a batch script?**

*Note: I don&#39;t want an infinite loop*

For example, here is what it would look like in Javascript:

```js
var i;
for (i = 0; i &lt; 100; i++) {
  console.log( i );
} 
```

**What would it look like in a batch script running on Windows?**

Batch script loop

In Scala, you often use an iterator to do a `for` loop in an increasing order like:

    for(i &lt;- 1 to 10){ code }

How would you do it so it goes from 10 to 1? I guess `10 to 1` gives an empty iterator (like usual range mathematics)?

I made a Scala script which solves it by calling reverse on the iterator, but it&#39;s not nice in my opinion, is the following the way to go?

    def nBeers(n:Int) = n match {

        case 0 =&gt; (&quot;No more bottles of beer on the wall, no more bottles of beer.&quot; +
                   &quot;\nGo to the store and buy some more, &quot; +
                   &quot;99 bottles of beer on the wall.\n&quot;)

        case _ =&gt; (n + &quot; bottles of beer on the wall, &quot; + n +
                   &quot; bottles of beer.\n&quot; +
                   &quot;Take one down and pass it around, &quot; +
                  (if((n-1)==0)
                       &quot;no more&quot;
                   else
                       (n-1)) +
                       &quot; bottles of beer on the wall.\n&quot;)
    }

    for(b &lt;- (0 to 99).reverse)
        println(nBeers(b))


Scala downwards or decreasing for loop?

Basically, I want to do something like this (in Python, or similar imperative languages):

    for i in xrange(1, 5):
        try:
            do_something_that_might_raise_exceptions(i)
        except:
            continue    # continue the loop at i = i + 1

How do I do this in Ruby? I know there are the `redo` and `retry` keywords, but they seem to re-execute the &quot;try&quot; block, instead of continuing the loop:

    for i in 1..5
        begin
            do_something_that_might_raise_exceptions(i)
        rescue
            retry    # do_something_* again, with same i
        end
    end

Ruby: Continue a loop after catching an exception

Is there an elegant way to skip the first iteration in a Java5 foreach loop ?

Example pseudo-code:

    for ( Car car : cars ) {     
       //skip if first, do work for rest
       .
       .
    }

java foreach skip first iteration

I want to skip the first 17 lines while reading a text file.

        
Let&#39;s say the file looks like:

    0
    0
    0
    0
    0
    0
    0
    0
    0
    0
    0
    0
    0
    0
    0
    0
    0
    good stuff

I just want the good stuff. What I&#39;m doing is a lot more complicated, but this is the part I&#39;m having trouble with.

Skip first couple of lines while reading lines in Python file

How do forcibly skip a unit test in Django?

@skipif and @skipunless is all I found, but I just want to skip a test right now for debugging purposes while I get a few things straightened out.

How do you skip a unit test in Django?

Talking about `Stream`s, when I execute this piece of code

	public class Main {
		public static void main(String[] args) {
			Stream.of(1,2,3,4,5,6,7,8,9)
			.peek(x-&gt;System.out.print(&quot;\nA&quot;+x))
			.limit(3)
			.peek(x-&gt;System.out.print(&quot;B&quot;+x))
			.forEach(x-&gt;System.out.print(&quot;C&quot;+x));
		}
	}

I get this output 

    A1B1C1
    A2B2C2
    A3B3C3

because limiting my stream to the first three components forces actions *A*, *B* and *C* to be executed only three times.

Trying to perform an analogous computation on the last three elements by using `skip()` method, shows a different behaviour: this

	public class Main {
		public static void main(String[] args) {
			Stream.of(1,2,3,4,5,6,7,8,9)
			.peek(x-&gt;System.out.print(&quot;\nA&quot;+x))
			.skip(6)
			.peek(x-&gt;System.out.print(&quot;B&quot;+x))
			.forEach(x-&gt;System.out.print(&quot;C&quot;+x));
		}
	}

outputs this

    A1
    A2
    A3
    A4
    A5
    A6
    A7B7C7
    A8B8C8
    A9B9C9

Why, in this case, actions *A1* to *A6* are being executed? It must have something to do with the fact that *limit* is a [short-circuiting stateful intermediate operation][1], while *skip* is not, but I don&#39;t understand practical implications of this property. Is it just that &quot;every action before *skip* is executed while not everyone before *limit* is&quot;?


  [1]: https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#limit-long-

Content Type	Original Author	Original Content on Stackoverflow
Question	Marcel	View Question on Stackoverflow
Solution 1 - C#	Mark Byers	View Answer on Stackoverflow
Solution 2 - C#	ChrisF	View Answer on Stackoverflow
Solution 3 - C#	TomTom	View Answer on Stackoverflow

LINQ: How to skip one then take the rest of a sequence

C# Problem Overview

C# Solutions

Solution 1 - C#

Solution 2 - C#

Solution 3 - C#

How to implement didReceiveMemoryWarning?

MYSQL sum() for distinct rows

Attributions