I am currently working on a simulation system so i've an array like
int[] arr = {2,5,9,10,0, 4,1,5,3};
I want array of indexes of values based on lower and output result like
result = {4, 6, 0, 8, 1, 7, 2, 3};
I searched all over for almost 3 days i can't find.
In the 2nd array you want the indexes of the elements in the first array as sorted in ascending order.
You can use LINQ to do this
int[] arr = { 2, 5, 9, 10, 0, 4, 1, 5, 3 };
int[] result = arr.Select((x, i) => (x, i))
.OrderBy(t => t.x)
.Select(t => t.i)
.ToArray();
Here, we used an overload of Select that yields the index:
Select<TSource,TResult>(IEnumerable, Func<TSource,Int32,TResult>).
The first Select creates a ValueTuple.
The test
Console.WriteLine(String.Join(", ", result));
Yields the result:
4, 6, 0, 8, 5, 1, 7, 2, 3
Note that the number 5 appears twice in the input array. Therefore, the result is ambiguous. (Your expected result has only 8 indexes but the input array has a length of 9)
My full .NET 6.0 test code (Console App):
namespace CoreConsoleApp;
internal static class SortedArrayIndexes
{
public static void Test()
{
// Indexes 0 1 2 3 4 5 6 7 8
int[] arr = { 2, 5, 9, 10, 0, 4, 1, 5, 3 };
int[] result = arr.Select((x, i) => (x, i))
.OrderBy(t => t.x)
.Select(t => t.i)
.ToArray();
Console.WriteLine(String.Join(", ", result));
}
}
It is called in my Main method with:
SortedArrayIndexes.Test();
Console.ReadKey();
In case you are working with an older Framework or language version, you can also use the older System.Tuple Class
int[] result = arr.Select((x, i) => new Tuple<int, int>(x, i))
.OrderBy(t => t.Item1)
.Select(t => t.Item2)
.ToArray();
arr.Select((x, i) => (x, i)) a local variable x cannot be declared in this scope Another error in last ) expectedx somewhere. Then replace x by something else (e.g. with v for value`). Also if you are using an older version of C# (<= 6.0), the ValueTuples will not work. Click on the ValueTuple link for more info. I added my full .NET 6.0 test code which is working.We can use the built-in Array.Sort() method. It has a second parameter that returns the sorted indices as well, but it requires us to make a new array with the indices (i.e. starts from 0 and ends at the length of the original array)
int[] arr = {2,5,9,10,0,4,1,5,3};
int[] indexArr = Enumerable.Range(0, arr.Length).ToArray();
Array.Sort(arr, indexArr);
Note that you will need to add using System.Linq; if you get an error that Enumerable doesn't exist.
