Compress Items in Array C#

Question

I have the following list:

List<int> Items = new List<int> { 0, 0, 1, 1, 0 }

I want same items in the array that are next to each other to continue to add up until the next item in the array that is not the same, with the output being the following:

0,2
1,2
0,1

This is the code I have:

    public static void Test()
    {
        StringBuilder Data = new StringBuilder();
        List<int> Items = new List<int> { 0, 0, 1, 1, 0 };
        int Index = 1;

        if (Items[0] != Items[1])
        {
            Data.AppendLine(Items[0] + " 1");
        }
        while (Index < Items.Count)
        {
            int PastValue = Items[Index - 1];
            int CurrentValue = Items[Index];
            int CurrentLength = 1;

            while (CurrentValue == PastValue && Index + CurrentLength < Items.Count)
            {
                CurrentValue = Items[Index + CurrentLength];
                CurrentLength += 1;
            }
            Data.AppendLine(CurrentValue + " " + CurrentLength);

            Index = Index + CurrentLength; 
        }
        Console.WriteLine(Data.ToString());
    }

And it produces the following which is incorrect:

1,2
0,2

Is there a better way of doing this? Any help much appreciated.

Hint: Don't do string math. Work out the math using integers and then produce the output you want. — John Alexiou
– John Alexiou, Commented Dec 28, 2022 at 1:59

Enigmativity · Accepted Answer · 2022-11-18 02:35:00Z

Let's start with this extension method:

public static IEnumerable<(V Value, int Count)> Compress<V>(this IEnumerable<V> source)
{
    var count = 0;
    var current = default(V);
    foreach (var value in source)
    {
        if (count == 0)
        {
            current = value;
            count = 1;
        }
        else
        {
            if (current.Equals(value))
            {
                count++;
            }
            else
            {
                yield return (current, count);
                current = value;
                count = 1;
            }
        }
    }
    if (count != 0)
    {
        yield return (current, count);
    }
}

Now I can write this:

List<int> Items = new List<int> { 0, 0, 1, 1, 0 };
List<(int Value, int Count)> output = Items.Compress().ToList();

That gives me:

To display that it becomes easy:

string display = String.Join(Environment.NewLine, output.Select(o => $"{o.Value},{o.Count}"));
Console.WriteLine(display);

That gives me:

0,2
1,2
0,1

Idle_Mind · Accepted Answer · 2022-11-24 17:37:28Z

Another one:

public static void Main(string[] args)
{
    List<int> Items = new List<int> { 0, 0, 1, 1, 0 };

    int count = 0;
    int prevInt = 0;
    List<Tuple<int, int>> results = new List<Tuple<int, int>>();            
    foreach(int i in Items)
    {
        if (count == 0 || i == prevInt)
        {
            count++;
        }
        else
        {
            results.Add(new Tuple<int, int>(prevInt, count));
            count = 1;
        }
        prevInt = i;
    }
    if (count > 0)
    {
        results.Add(new Tuple<int, int>(prevInt, count));
    }

    String result = String.Join(Environment.NewLine, results);
    Console.WriteLine(result);
    Console.WriteLine("Press Enter to Quit.");
    Console.ReadLine();
}

Output:

(0, 2)
(1, 2)
(0, 1)
Press Enter to Quit.

mkmkmk · Accepted Answer · 2022-11-18 02:24:07Z

0

 public static void Test()
        {
            StringBuilder Data = new StringBuilder();
            List<int> Items = new List<int> { 0, 0, 1, 1, 0 };
            int tempCount = 0;
            int tempNumber = 0;
            for ( int i = 0; i < Items.Count; i++ )
            {
                if ( Items[i].Equals(tempNumber) )
                {
                    tempCount++;
                }
                else
                {
                    if(tempCount>0)
                    {
                        Data.AppendLine( tempNumber + "," + tempCount );
                    }
                    tempNumber = Items[i];
                    tempCount = 1;
                }
            }
            Data.AppendLine( tempNumber + "," + tempCount );
            Console.WriteLine( Data.ToString() );
        }

answered Nov 18, 2022 at 2:24

mkmkmk

1974 bronze badges

1 Comment

Jonathan Barraone Over a year ago

This is awesome! Thank you so much, it works perfectly. I don't know why someone downvoted it.

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