Array Index selection

Question

I have a array of length 300 of type int. Most of the element is 0 and I want to get the index of the first element that is greater than 0. How can I achieve this.

Kriz

Answer 1

Hi, there is no method for retreiving Index of an array for some predicate (first element > 0).

So for this you can have multiple approaches, but most elementary approach is with loop and condition in loop.

This is sample for that:

int[] array = new int[300];
//some code here for filling up the array

int firstIndex = -1;

for (int i = 0; i < array.Length; i++)
{
    if (array[i] > 0)
    {
         firstIndex = i;
         break; //no neeed for loop any more
    }
}

//now you can use result in firstIndex variable, if it is -1 than item is not found for predicate inside for loop (array[i] > 0)

If you were looking for first index of some value in array than things is much simplier because method exists for this - IndexOf - static method of Array class

So for this scenario you can write this:

 int[] array = new int[300];
//you should fill up array with something
int firstIndex = Array.IndexOf(array, 1);

Also if you are looking for last index in array for some value you have LastIndexOf method. For both methods you have also strongy typed (generic) varsion.

Hope that it helps

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Answer 2

Hi,

//assume this array list contains 300 records
ArrayList arr = LoadData(); 
int greaterIndex = -1;
int arrValue = -1;
for(int i = 0;i<arr.Length;i++)
{
  if(int.Parse(arr[i].ToString()) > 0)
  {
     //if you want index then 
     greaterIndex = i;

     //if you want the value then
     arrValue = int.Parse(arr[i].ToString());
       break;
  }
}
Console.WriteLine(greaterIndex);
Console.WriteLine(arrValue);

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Nagarjuna Dilip

Answer 3

 List<int> myArray = new List<int>
                                    {
                                        0,
                                        1,
                                        0
                                    };
           int index = myArray.IndexOf( myArray.First(x => x > 0));

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Mark Answered, if it solves your question and Vote if you found it helpful.
Rohit Arora