Develop Reference

Determine if array contains all zeroes

I create the following array like this:
array<UInt16>^ temp = gcnew array<UInt16>(1000);
How do I determine if this entire array has been filled with zero or not.
I think I may be able to use TrueForAll(T) but I'm not sure.

var allElementsAreZero = temp.All(o => o == 0);
Simple as that.
It'll return when it finds one that doesn't satisfy the condition, so may not necessarily iterate through your whole collection:
"The enumeration of source is stopped as soon as the result can be determined."
https://msdn.microsoft.com/en-us/library/bb548541(v=vs.110).aspx

This should work properly (here I used LINQ):
IEnumerable<int> values = new List<int>(); // Or use any array type instead of List.
... Add your values here ...
var allAreZero = !values.Any(v => v != 0);
P.S. the array class inherits IEnumerable.
And here is a solution with foreach:
var isAllZero = true;
foreach (var value in values)
{
if (value != 0)
{
isAllZero = false;
break;
}
}
UPDATE
The really difference between TrueForAll, and my LINQ code is: LINQ code uses the fluent (or maybe also query) syntax, where TrueForAll is just a normal function where you send the array as a parameter.

initialize a counter from 0 then use for loop to interate through the array and increment the counter whenever it finds 0, and at the end compare the counter with size of array if its equal, it has all zeros

Reading the C++/CLI specification, it has been filled with
0s because you created it with a "new-expression" and the default value of the element type is 0.
24.2 CLI array creation
CLI array instances are created by new-expressions containing gcnew (§15.4.6) or …
Elements of CLI arrays created by new-expressions are always initialized to their default value.

Why do I get an error when List<object>.Add(int)

I have an array of List types:
List<object>[] vector = new List<object>[3];
The first List contains strings:
// Get word lists together, remove duplicates
var words = tableA.ToList().Union(tableB.ToList());
// Sort words
words = words.OrderBy(s => s, StringComparer.CurrentCultureIgnoreCase);
// Add words to the vector first slot
vector[0] = words.ToList<object>();
Now, I want to add ints to the second and third lists, but I get an error here:
vector[1].Add(tableA.GetValue(keyword));
vector[2].Add(tableB.GetValue(keyword));
GetValue() returns an int. But when I add these ints to the vector Lists it throws error:
ERROR Caught: Object reference not set to an instance of an object.
How should I add the ints to the List? Or is there some other data structure I should use instead for the vector? I feel there is some trivial cast I'm missing but I haven't been able find a solution.

I'm not an expert in C#, but i think i understand.
When you write :
List<object> vector = new List<object>[3];
you create a table of List with a size of 3.
You can put something into each slot of this array, but each "slot" still refers to no instance after this first line of code.
When you write
vector[0] = words.ToList<object>();
You put somehting into the first slot of vector list. But [1] and [2] are still empty. And
vector[1]
refers to a reference not set to an instance of an object. In short terms, it refers to nothing.

You must initialize each vector index value before add value. Thanks

When writing var a = new List<object> you´re only declaring that a is a list holding some (in your case three) items. However you don´t determine what stands in those three elements. You´d have to out some values into every single item, before you can anything with it (e.g. call any method).
You´re allready putting a list into the first item, however the elements on index one and two remain null causing a NullReferenceException when calling a method like the following:
vector[1].Add(...);
So you should initialize the value at index oe and two before:
vector[1] = new List<int>();
vector[2] = new List<int>();
But still you can´t do much with the list, because it is of type object, so you´d have to cast every element to the actual type:
((List<int>)vector[1]).Add(myInt);
Anyway I doubt storing three completely different lists within one single list alltogether is a good idea. Maybe you should define a class with the three lists as members instead:
class MyClass
{
public List<string> Words { get; set; }
public List<int> NumbersA { get; set; }
public List<int> NumbersB { get; set; }
}

Sort one List<> based on another

Say I have
List<int> ages = new List<int>() { 8, 5, 3, 9, 2, 1, 7 };
List<int> marks = new List<int>() { 12, 17, 08, 15, 19, 02, 11 };
I can sort my marks by ages like this:
while (true)
{
bool swapped = false;
for (int i = 0; i < ages.Count - 1; i++)
if (ages[i] > ages[i + 1])
{
int tmp = ages[i];
ages[i] = ages[i + 1];
ages[i + 1] = tmp;
tmp = marks[i];
marks[i] = marks[i + 1];
marks[i + 1] = tmp;
swapped = true;
}
if (!swapped)
break;
}
Now I want to put this into a function that accepts any two lists. The first parameter will be the reference list, the numerical or comparable list. The second parameter will be the list containing the data.
For example:
public static void Sort<T>(List<T> RefList, List<T> DataList)
{
// sorting logic here...
}
There are a few problems:
First of all, T is almost certainly not the same type in RefList and DataList. RefList might be dates, integers, or doubles; whereas DataList is free to be absolutely anything. I need to be able to receive two, arbitrary generic types.
Secondly, I cannot seem to use the > operator with the T in this line:
if (ages[i] > ages[i + 1])
Perhaps my whole approach is wrong.
By the way, I have read responses to similar questions that suggest that the two lists should be combined into a single list of a compound data type. This isn't practical at all for my application. All I want to do is write a static function that somehow sorts one list based on the elements of another.

To sort one list the way you want you actually need to somehow keep references from items in first list to they weight/keys in the second list. No existing methods do that as you can't easily associate metadata with arbitrary values (i.e. if first list is list of int as in your case there is nothing to map to keys in second list). Your only reasonable option is to sort 2 lists at the same time and make association by index - again no existing classes to help.
It may be much easier to use solution that you reject. I.e. simply Zip and OrderBy, than recreate first list:
ages = ages
.Zip(marks, (a,m)=> new {age = a; mark = m;})
.OrderBy(v => v.mark)
.Select(v=>v.age)
.ToList();
Note (courtesy of phoog): if you need to do this type of sorting with Array there is Array.Sort that allows exactly this operatiion (see phoog's answer for details).

There's no framework method to do this with List<T>, but if you don't mind putting the data into two arrays, you can use one of the Array.Sort() overloads that takes two arrays as arguments. The first array is the keys, and the second is the values, so your code might look like this (leaving aside the step of getting arrays from the lists):
Array.Sort(ages, marks);
The specifics of getting the values into arrays and then back into lists would depend, among other things, on whether you need to end up with the same list sorted appropriately or whether it's okay to return a new list with the data in the desired order.

Use:
public static void Sort<TR, TD>(IList<TR> refList, IList<TD> dataList)
where TR : System.IComparable<TR>
where TD : System.IComparable<TD>
{
...
}
and then use:
refList[i].CompareTo(refList[i+1])
instead of the operators.
.Net numbers already implement IComparable, and you can use overloads that allow you to specify a different IComparable.

If I understand "I can sort my marks by ages like this:" properly,
I would like to suggest the below to eliminate much confusion.
struct Student{
int age;
int marks;
};
List<Student> students = {{8,12}, ...};
Now you can sort according to age and marks is accordingly sorted automatically.
If it is not possible, you need to fix the code as below.
First of all, T is almost certainly not the same type in RefList and DataList.
Then you need 2 parameters T1, T2. Just T implies the types are the same.
public static void Sort<RefType, DataType>(List<RefType> RefList, List<DataType> DataList)
{
You can also zip the two lists together as suggested by Mechanical Snail and explained in Looping through 2 Lists at once

Cannot implicitily convert type `double[]` to `System.Collections.Generic.List<double>`

I am getting the following error message with the code below. I thought the data type List<double> was the same as double[] but that C# required it to be instantiated using the first syntax for the variable to work as an object. What am I doing wrong or is my thinking wrong?
Cannot implicitily convert type `double[]` to `System.Collections.Generic.List<double>`
Code:
private void RunScript(List<Curve> crv, double nb, ref object DivPts)
{
List<double> nbtemp = new List<double>();
List<double> Divpt = new List<double>();
for(int i = 0; i < crv.Count;i = i + 2)
{
nbtemp = crv[i].DivideByLength(nb, true);
}
Divpt = nbtemp;

No, a list is not an array, even though the concepts are somewhat similar. The List<T> class in C# is actually implemented with a behind-the-scenes array.
If you want to set a List from an array, you can use something like this:
nbtemp = new List<double>(crv[i].DivideByLength(nb, true));
that will create a new List, and initialize it with the array. You can also use the AddRange method of the List, if you would like to append an array to an existing list, like this:
nbtemp.AddRange(crv[i].DivideByLength(nb, true));

You can't convert from Array to List, but you can easily call:
nbtemp = crv[i].DivideByLength(nb, true).ToList();
Or, since you already have to Lists defined, you could also:
nbtemp.AddRange(crv[i].DivideByLength(nb, true));

You are using an assignment and it is hard to tell what DivideByLength returns, if a single value then use:
nbtemp.Add(crv[i].DivideByLength(nb, true));
Otherwise, if it is returning an array, try changing your definition to allow the list to contain arrays:
List<double[]> nbtemp = new List<double[]>();
Note that List is not equivalent to double[]. List has many features that a simple array does not. You can see the differences by looking at the two different MSDN articles for which methods are publicly exposed.
List
Array
Also, your for loop as it stands is using an assignment. Without a change to that part of the code, you will only assign the last iteration of the for loop to the variable nbtemp (assuming you remove the error)

They are both IEnumerable implementers but they are not equivalent types. You will need to perform a cast or a method call. In the code above I would say you'd need:
nbtemp = (crv[i].DivideByLength(nb, true)).ToList();
or
nbtemp.AddRange(crv[i].DivideByLength(nb, true));

How delete an item from struct array in C#

I have a struct in C# and I define and array list of my struct based on my code that I express here. I add items in my array list, but I need to delete a few rows from my list too. Could you help me how can I delete item or items from my struct array list:
public struct SwitchList
{
public int m_Value1, m_Value2;
public int mValue1
{
get { return m_Value1; }
set {m_Value1 = value; }
}
public int mValue2
{
get { return m_Value2; }
set {m_Value2 = value; }
}
}
//Define an array list of struct
SwitchList[] mSwitch = new SwitchList[10];
mSwitch[0].mValue1=1;
mSwitch[0].mValue2=2;
mSwitch[1].mValue1=3;
mSwitch[1].mValue2=4;
mSwitch[2].mValue1=5;
mSwitch[2].mValue2=6;
Now how can I delete one of my items, for example item 1.
Thank you.

Arrays are fixed length data structures.
You will need to create a new array, sized one less than the original and copy all items to it except the one you want to delete and start using the new array instead of the original.
Why not use a List<T> instead? It is a dynamic structure that lets you add and remove items.

You will need to move elements around and resize the array (which is expensive), since there is some complexity there you going to want to hide it in class that just presents the collection without exposing the implementation details of how its stored. Fortunately Microsoft has already provided a class that does just this called List<T> which along with a few other collection types in System.Collections.Generic namespace meet most common collection needs.
as a side note, you should use auto-properties instead of the trivial property style that you ha

That's not possible, because an array is a fixed size block of elements. Because structs are values types and not reference types, you also can't just set the element zo null. One option would be to create a new smaller array and to copy your remaining values to the new array. But the better approach would be to use a List in my opinion.

If you really, really want to use arrays and move things around, here are some examples of how to do it:
{
// Remove first element from mSwitch using a for loop.
var newSwitch = new SwitchList[mSwitch.Length - 1];
for (int i = 1; i < mSwitch.Length; i++)
newSwitch[i - 1] = mSwitch[i];
mSwitch = newSwitch;
}
{
// Remove first element from mSwitch using Array.Copy.
var newSwitch = new SwitchList[mSwitch.Length - 1];
Array.Copy(mSwitch, 1, newSwitch, 0, mSwitch.Length - 1);
mSwitch = newSwitch;
}