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How do you compute for the moving average of a given dataset in C#?

So I use a randomly generated dataset and I need to find the moving average of the sample size the user inputted. For example, the dataset is a list with {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} and the sample size the user inputted is 2. The program must calculate first the mean of:
1 and 2 = 1.5, 2 and 3 = 2.5, 3 and 4 = 3.5,
and so on. How do I do this? Thanks! 😊

You can keep track of the sum and queue up all the values so you know what to subtract from the sum once you get to the sample size.
public static IEnumerable<decimal> MovingAverages(IEnumerable<decimal> values, int sample)
{
var queue = new Queue<decimal>(sample);
decimal sum = 0;
foreach(var x in values)
{
sum += x;
queue.Enqueue(x);
if(queue.Count == sample)
{
yield return sum / sample;
sum -= queue.Dequeue();
}
}
}
Basically this will queue up the first n values (equal to sample) and the sum. Once it gets the desired number of values to average it yields the sum divided by the sample size and then removes the oldest value from the queue and subtracts it from the sum. Note that if the sample size is larger than the number of values this will return an empty enumerable.

This can be done with a simple loop.
for (int i = 0; i <= array.Length - samplesize; i++)
Console.WriteLine(array.Skip(i).Take(samplesize).Average());
The Skip(i).Take(samplesize) portion selects only the elements you are interested in at the moment.

Finding all possible combinations of int[] array, constrained by length in C#

int[] listOfValues = {1, 2, 5, 2, 6};
I need to be able to find all pair combinations of this array, including repetitions. Each value in the array comes from a deck of cards. So, if the value "2" appears twice in the array, for example, we can assume that these are two different values, and as such, need to be treated separately.
Sample of expected pairs of cards:
{1, 2}
{1, 2}
{2, 1}
{2, 1}
{2, 2}
{1, 5}
{1, 6}
etc.......
These separate int[] results will then need to be added to a List (if you can even add duplicate int[] values to a list, that is!), once all possible values have been found.
I have looked for a few hours online, and can't seem to get any of the solutions working for my particular task.
Does anyone have any ideas please?

You should really do homework on your own. Or at least try it first. You haven't provided code, so I cannot ethically give you the full solution.
However, this will get you started:
Think about it as if you were to do it by hand. Most people would pick the first value and the second value and write them down. Then they would write that pair backwards. Then they would do the first value and the third, then backwards, and so on and so on.
It would look something like:
{1,2}
{2,1}
{1,5}
{5,1}
{1,2}
{2,1}
{1,6}
{6,1}
{2,5} -Now we iterate again, starting with the second value
So how would we express that in code? Nested loops!
Here is the skeleton of an algorithm to solve your problem:
List<int[]> pairs = new List<int[]>();
for(int x = 0; x < listOfValues.Length - 1; x++)
{
for(int y = x+1; y < listOfValues.Length; y++)
{
// Create an array of the [x] position and [y] position of listOfValues
// Create another array, except swap the positions {[y],[x]}
// Add both arrays to the "pairs" List
}
}
Try to understand what this code is doing. Then fill in the blanks. You should get the correct answer. Always make sure to understand why, though. Also, try to see if you can figure out any improvements to this code.

With linq you could do it this way.
int[] listOfValues = { 1, 2, 5, 2, 6 };
var combination = listOfValues.Select(i => listOfValues.Select(i1 => new Tuple<int, int>(i, i1)).ToList())
.ToList()
.SelectMany(list => list.Select(x => x)).ToList();

With thanks to Clay07g's post, I was able to resolve the problem with the following code:
public static List<int[]> getCardCombos(int[] values)
{
List<int[]> pairs = new List<int[]>();
for (int x = 0; x < values.Length - 1; x++)
{
for (int y = x + 1; y < values.Length; y++)
{
int firstValue = values[x];
int secondValue = values[y];
// Create an array of the [x] position and [y] position of listOfValues
int[] xAndY = { firstValue, secondValue};
// Create another array, except swap the positions {[y],[x]}
int[] yAndX = { secondValue, firstValue };
pairs.Add(xAndY);
pairs.Add(yAndX);
// Add both arrays to the "pairs" List
}
}
return pairs;
}

c# foreach loop not able to add literals in an array

Firstly I know that I can't use a foreach loop in C# to add values in let's say an array... But why? Why for example I can't do this
int[] numbers = { 1, 4, 3, 5, 7, 9 };
foreach (int item in numbers)
{
numbers[item] = 2;
}
Does it have something to do with the actual realisation of the foreach loop in the back-end? And how does the foreach loop exactly work? I know that it goes through the whole collection(array) but how exactly?

You are passing in the value of an item (your variable, item, will be the value of the array at each position in sequence, not the index) in the array as the index. The index used there is meant to be the position of the item you are attempting to access, not the value. So each iteration of the loop you are calling:
numbers[1]
numbers[4]
numbers[3]
numbers[5]
numbers[7]
numbers[9]
The array has 6 numbers, so when you get to numbers[7], you are asking for a value that is not there, hence the exception.
A better method of doing what you are trying to do would be:
for(int i = 0; i < numbers.Length; i++)
{
numbers[i] = 2;
}
On each iteration of this loop you would be accessing:
numbers[0]
numbers[1]
numbers[2]
numbers[3]
numbers[4]
numbers[5]

I'm looking at this:
numbers[item] = 2;
In this expression, you're using the item variable like an index, as if it had the values 1, 2, 3, 4, etc. That's not how the foreach iteration variable works for C#. The only language I know that does it this way is Javascript.
Remember that foreach and for are not the same thing. Just about every other language, including C#, gives you the actual array values in the item variable of a foreach loop: 1,4, 3, 5 etc. Now, these are integers, so you could try to use them as indexes. You can run the loop for a while like that... until you get to the value 7. At this point, your array only has six values. You're trying to do this:
numbers[7] = 2;
for an array where the largest valid index you can use is 5.
This is true even taking your modification of the array into account. Let's look at the array after each iteration through the loop:
{ 1, 4, 3, 5, 7, 9 } //initial state
{ 1, 2, 3, 5, 7, 9 } // after 1st iteration (index 0). Value at index 0 is 1, so item as index 1 is set to 2
{ 1, 2, 2, 5, 7, 9 } // after 2nd iteration (index 1). Value at index 1 is now 2, so item at index 2 is set to 2
{ 1, 2, 2, 5, 7, 9 } // after 3rd iteration (index 2). Value at index 2 is now 2, so item at index 2 is set to 2
{ 1, 2, 2, 5, 7, 2 } // after 4th iteration (index 3). Value at index 3 is 5, so item at index 5 is set to 2
// The 5th iteration (index 4). Value at index 4 is 7, which is beyond the end of the array
For the why of this... it sounds like you're used to a more dynamic language. Some these other languages, like php or Javascript, don't have real arrays at all in the pure computer science sense. Instead, they have collection types they'll call an array, but when you get down to it are really something different.
C# has real arrays, and real arrays have a fixed size. If what you really want is a collection, C# has collections, too. You can use List<T> objects, for example, to get an array-like collection you can append to easily.
For the other languages, the results vary depending on what you're talking about, but for the most permissive the result of your 5th iteration is something like this:
{ 1, 2, 2, 5, 7, 2, ,2 }
Note the missing value at index 6. That kind of things leads to mistakes that slip through your tests and don't show up until run-time. You also need to start wondering just how densely or sparsely the array will be filled, because the best strategy for handling these arrays can vary wildly depending on your answer... everything from just a big backing array with empty nodes that the programmer has to know about all the way to Hashtables and Dictionaries. And, by the way, C# again has these options available to you.

You need to step through your code in a debugger.
A for statement is more like a while statement, not like a foreach.
The line int[] numbers = { 1, 4, 3, 5, 7, 9 }; create this:
numbers[0] = 1;
numbers[1] = 4;
numbers[2] = 3;
numbers[3] = 5;
numbers[4] = 7;
numbers[5] = 9;
Your foreach statement does this:
numbers[1] = 2;
numbers[4] = 2;
numbers[3] = 2;
numbers[5] = 2;
numbers[7] = 2; <- this line overflows your array!
numbers[9] = 2; <- and so would this.
You have to learn the difference between an array index and an array value.

You need to create counter, in other case you trying to access item outside of array
int[] numbers = new int[]{ 1, 4, 3, 5, 7, 9 };
int i = 0;
foreach (int item in numbers)
{
numbers[i] = 2;
i++;
}
// Print the items of the array
foreach (int item in numbers)
{
Console.WriteLine(item);
}

Find smallest number in given range in an array

Hi i have an array of size N. The array values will always have either 1, 2, 3 integer values only. Now i need to find the lowest number between a given range of array indices. So for e.g. array = 2 1 3 1 2 3 1 3 3 2. the lowest value for ranges like [2-4] = 1, [4-5] = 2, [7-8] = 3, etc.
Below is my code :
static void Main(String[] args) {
string[] width_temp = Console.ReadLine().Split(' ');
int[] width = Array.ConvertAll(width_temp,Int32.Parse); // Main Array
string[] tokens_i = Console.ReadLine().Split(' ');
int i = Convert.ToInt32(tokens_i[0]);
int j = Convert.ToInt32(tokens_i[1]);
int vehicle = width[i];
for (int beg = i+1; beg <= j; beg++) {
if (vehicle > width[beg]) {
vehicle = width[beg];
}
}
Console.WriteLine("{0}", vehicle);
}
The above code works fine. But my concern is about efficiency. In above I am just taking one set of array range, but in actual there will be n number of ranges and I would have to return the lowest for each range. Now the problem is if there is a range like [0-N], N is array size, then I would end up comparing all the items for lowest. So I was wondering if there is a way around to optimize the code for efficiency???

I think it is a RMQ (Range Minimum Query) and there is several implementation which may fit your scenario.
Here is a nice TopCoder Tutorial cover a lot of them, I recommend two of them:
Using the notation in the tutorial, define <P, T> as <Preprocess Complexity, Query Complexity>, there is two famous and common implementation / data structure which can handle RMQ: Square Rooting Array & Segment Tree.
Segment Tree is famous yet hard to implement, it can solve RMQ in <O(n), O(lg n)> though, which has better complexity than Square Rooting Array (<O(n), O(sqrt(n))>)
Square Rooting Array (<O(n), O(sqrt(n))>)
Note That It is not a official name of the technique nor any data structure, indeed I do not know if there is any official naming of this technique since I learnt it...but here we go
For query time, it is definitely not the best you can got to solve RMQ, but it has an advantage: Easy Implementation! (Compared to Segment Tree...)
Here is the high level concept of how it works:
Let N be the length of the array, we split the array into sqrt(N) groups, each contain sqrt(N) elements.
Now we use O(N) time to find the minimum value of each groups, store them into another array call M
So using the above array, M[0] = min(A[0..2]), M[1] = min(A[3..5]), M[2] = min(A[6..8]), M[3] = min(A[9..9])
(The image from TopCoder Tutorial is storing the index of the minimum element)
Now let's see how to query:
For any range [p..q], we can always split this range into 3 parts at most.
Two parts for the left boundaries which is some left over elements that cannot be form a whole group.
One part is the elements in between, which forms some groups.
Using the same example, RMQ(2,7) can be split into 3 parts:
Left Boundary (left over elements): A[2]
Right Boundary (left over elements): A[6], A[7]
In between elements (elements across whole group): A[3],A[4],A[5]
Notice that for those in between elements, we have already preprocessed their minimum using M, so we do not need to look at each element, we can look and compare M instead, there is at most O(sqrt(N)) of them (it is the length of M afterall)
For boundary parts, as they cannot form a whole group by definition, means there is at most O(sqrt(N)) of them (it is the length of one whole group afterall)
So combining two boundary parts, with one part of in between elements, we only need to compare O(3*sqrt(N)) = O(sqrt(N)) elements
You can refer to the tutorial for more details (even for some pseudo codes).

You could do this using Linq extension methods.
List<int> numbers = new List<int> {2, 1, 3, 1, 2, 3, 1, 3, 3, 2};
int minindex =1, maxindex =3, minimum=-1;
if(minindex <= maxindex && maxindex>=0 && maxindex >=0 && maxindex < numbers.Count())
{
minimum = Enumerable.Range(minindex, maxindex-minindex+1) // max inclusive, remove +1 if you want to exclude
.Select(x=> numbers[x]) // Get the elements between given indices
.Min(); // Get the minimum among.
}
Check this Demo

This seems a fun little problem. My first point would be that scanning a fixed array tends to be pretty fast (millions per second), so you'd need a vast amount of data to warrant a more complex solution.
The obvious first thing, is to break from the loop when you have found a 1, as you've found your lowest value then.
If you want something more advanced.
Create a new array of int. Create a pre load function that populates each item of this array with the next index where it gets lower.
Create a loop that uses the new array to skip.
Here is what I mean. Take the following arrays.
int[] intialArray = new int[] { 3, 3, 3, 3, 2, 2, 2, 1 };
int[] searchArray = new int[] { 4, 4, 4, 4, 7, 7, 7, 7 };
So the idea is to find the lowest between positions 0-7.
Start at initialArray[0] and get value 3.
Read searchArray[0] and get the value 4. The 4 is the next index where the number is lower.
Read initialArray[4] and get the value 2.
etc.
So basically you'd need to put some effort to build the searcharray, but onces it's complete you would scan each range much faster.

Form your looping like the following:
int[] inputArray = { 2, 1, 3, 1, 2, 3, 1, 3, 3, 2 };
int minIndex = 2;
int maxIndex = 5;
int minVal = 3;
for (int i = minIndex; i <= maxIndex; i++)
{
if (inputArray[i] <= minVal)
minVal = inputArray[i];
}
Console.WriteLine("Minimum value in the Given range is ={0}", minVal);

Efficiently adding multiple elements to the start of a List in C#

I have a list that I would like to add multiple elements to the start of. Adding to the start is linear time because it is backed by an array and has to be moved one at a time, and I cannot afford to do this as many times as I would have to if I implemented this the naive way.
If I know exactly how many elements I am about to add, can I shift them all that much so that the linearity only has to happen once?
List<int> myList = new List<int> { 6, 7, 8, 9, 10 };
//Desired list: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
//Unacceptable
for (int i = 5; i>=0; i--){
myList.Insert(0,i);
}
//Is this concept possible?
int newElements = 5;
for (int i = myList.Count; i>=0; i--){
myList[i+newElements] = myList[i];//This line is illegal, Index was out of range
}
for (int i = 0; i< newElements; i++){
myList[i] = i+1;
}
In this specific instance, access needs to be constant time, hence the usage of List. I need to be able to add elements to both the start and end of the data structure as fast as possible. I am okay with O(m) where m is the number of elements being added (since I don't think that can be avoided) but O(m*n) where n is the number of elements in the existing structure is far too slow.

You can use InsertRange which will be linear if the inserted collection implements ICollection<T>:
var newElements = new[] { 0, 1, 2, 3, 4 };
myList.InsertRange(0, newElements);

myList.InsertRange(0, new List<int> { 1, 2, 3, 4, 5 });

If your new elements are already in a List, you could use List.AddRange to add your "old" list to the end of the to-be-added-items-list.

I would imagine myList.InsertRange(0, newElements) would suit you well. Microsoft will have made that as efficient as it can be.