C# - 获取数组最后一个非零数的索引

Question

I have an array of annual results which I would like to identify the index of the last non-zero value. The 0 values at the end are an artifact of how the data is provided and read in. The 0 values can appear anywhere in the data, possibly even all 0s.

decimal[] results = { 0, 0, 39.59m, -17.83m, 73.52m, 0, 56.80m, -61.54m, 0, 0, 0, 0 }

I've tried a few things but I keep ending up with the index of the value before the zero in the middle (eg 4, not 7).

Answer 1

Here's the LINQ answer:

var index = results.Reverse().SkipWhile( x => x == 0 ).Count() - 1

Answer 2

decimal[] results = { 0, 0, 39.59m, -17.83m, 73.52m, 0, 56.80m, -61.54m, 0, 0, 0, 0 };

This approach uses a minimum of code

var index = Array.FindLastIndex(results, value => value != 0);

This approach gives you both the value and the index

var lastIndexAndValue = results
  .Select((value, index) => (index, value))
  .LastOrDefault(item => item.value != 0);

Answer 3

You can create an extension method which can generically handle LastIndexOf functionality.

public static class CustomExtensions
{
    public static int LastIndexOf<T>(this T[] input, Func<T, bool> selector) where T : IComparable<T>
    {
        int lastIndex = -1;

        for (int index = 0; index < input.Length; index++)
        {
            if (selector(input[index]))
            {
                lastIndex = index;
            }
        }

        return lastIndex;
    }
}

With this, you're essentially only updating the lastIndex variable if the value at the index matches the condition (ie not equal to 0)

Usage

decimal[] results = { 0, 0, 39.59m, 17.83m, 73.52m, 0, 76.80m, 61.54m, 0, 0, 0, 0 };

int index = results.LastIndexOf(num => num != 0);

// Output is 7

Answer 4

You will probably need to iterate through the array with a for loop. This should work:

int LastNonZero = -1;
for (int count = 0; count < results.Length; count++) {
  if (results[count] != 0) // It isn't zero:
  {
    LastNonZero = count;
  }
}

I just tested this and it returned 7.

Answer 5

I would just convert to List and use linq .

var result = results.ToList().LastIndexOf(results.Last(c=> c != 0));

If you do not want to convert to list.

var index = Array.LastIndexOf(results,results.Last(c=> c != 0));