CODEWITHSUNDEEP
c#enum-flags
EKS
EKS

Reputation: 5623

How do I get all possible combinations of an enum ( Flags )

[Flags]
public enum MyEnum
{
    None = 0,
    Setting1 = (1 << 1),
    Setting2 = (1 << 2),
    Setting3 = (1 << 3),
    Setting4 = (1 << 4),
}

I need to be able to somehow loop over every posible setting and pass the settings combination to a function. Sadly I have been unable to figure out how to do this

Upvotes: 8

Views: 7845

Answers (8)

Guvante
Guvante

Reputation: 19203

Not tested, use at your own risk, but should solve the problem generically enough. System.Enum is not a valid restriction as technically C# only allow inheritance in/with class the backend bypasses this for Enum and ValueType. So sorry for the ugly casting. It is also not horribly efficient but unless you are running this against a dynamically generated type it should only ever have to be done once per execution (or once period if saved).

public static List<T> GetAllEnums<T>()
    where T : struct
    // With C# 7.3 where T : Enum works
{
    // Unneeded if you add T : Enum
    if (typeof(T).BaseType != typeof(Enum)) throw new ArgumentException("T must be an Enum type");

    // The return type of Enum.GetValues is Array but it is effectively int[] per docs
    // This bit converts to int[]
    var values = Enum.GetValues(typeof(T)).Cast<int>().ToArray();

    if (!typeof(T).GetCustomAttributes(typeof(FlagsAttribute), false).Any())
    {
        // We don't have flags so just return the result of GetValues
        return values;
    }

    var valuesInverted = values.Select(v => ~v).ToArray();
    int max = 0;
    for (int i = 0; i < values.Length; i++)
    {
        max |= values[i];
    }

    var result = new List<T>();
    for (int i = 0; i <= max; i++)
    {
        int unaccountedBits = i;
        for (int j = 0; j < valuesInverted.Length; j++)
        {
            // This step removes each flag that is set in one of the Enums thus ensuring that an Enum with missing bits won't be passed an int that has those bits set
            unaccountedBits &= valuesInverted[j];
            if (unaccountedBits == 0)
            {
                result.Add((T)(object)i);
                break;
            }
        }
    }

    //Check for zero
    try
    {
        if (string.IsNullOrEmpty(Enum.GetName(typeof(T), (T)(object)0)))
        {
            result.Remove((T)(object)0);
        }
    }
    catch
    {
        result.Remove((T)(object)0);
    }

    return result;
}

This works by getting all the values and ORing them together, rather than summing, in case there are composite numbers included. Then it takes every integer up to the maximum and masking them with the reverse of each Flag, this causes valid bits to become 0, allowing us to identify those bits that are impossible.

The check at the end is for missing zero from an Enum. You can remove it if you are fine with always including a zero enum in the results.

Gave the expected result of 15 when given an enum containing 2,4,6,32,34,16384.

Upvotes: 7

g.pickardou
g.pickardou

Reputation: 35822

Concluded with this version:

Without checks:

public IEnumerable<T> AllCombinations<T>() where T : struct
{
    var type = typeof(T);
    for (var combination = 0; combination < Enum.GetValues(type).Cast<int>().Max()*2; combination++)
    {
        yield return (T)Enum.ToObject(type, combination);
    }
}

With some checks:

public IEnumerable<T> AllCombinations<T>() where T : struct
{
    var type = typeof(T);
    if (!type.IsEnum)
    {
        throw new ArgumentException($"Type parameter '{nameof(T)}' must be an Enum type.");
    }

    for (var combination = 0; combination < Enum.GetValues(type).Cast<int>().Max()*2; combination++)
    {
        var result = (T)Enum.ToObject(type, combination);

        // Optional check for legal combination.
        // (and is not necessary if all flag a ascending exponent of 2 like 2, 4, 8...
        if (result.ToString() == combination.ToString() && combination != 0)
        {
            continue;
        }

        yield return result;
    }
}

Upvotes: 0

Enrique Ramos
Enrique Ramos

Reputation: 36

I'm probably a little late to the party I would like to leave my solution which also includes the values plus the possible text of the combination in form of ("V1 | V2", "V1 | V2 | V3", etc).

I took some aspects of the solutions proposed above, so thanks to all that had posted the previous answers :D.

Note: only work with Enum set as base 2 combinations.

public static Dictionary<int,string> GetCombinations( this Enum enu)
    {
        var fields = enu.GetType()
                        .GetFields()
                        .Where(f => f.Name != "value__")
                        .DistinctBy(f=> Convert.ToInt32(f.GetRawConstantValue()));

        var result = fields.ToDictionary(f=>Convert.ToInt32(f.GetRawConstantValue()), f => f.Name);

        int max = Enum.GetValues(enu.GetType()).Cast<int>().Max();
        int upperBound = max * 2;

        for (int i = 0 ; i <= upperBound ; i += 2)
        {
            string s = Convert.ToString(i, 2).PadLeft(Math.Abs(i-max),'0');
            Boolean[] bits = s.Select(chs => chs == '1' ? true : false)
                             .Reverse()
                             .ToArray();

            if (!result.ContainsKey(i))
            {
                var newComb = string.Empty;
                for (int j = 1; j < bits.Count(); j++)
                {
                    var idx = 1 << j;
                    if (bits[j] && result.ContainsKey(idx))
                    {
                        newComb = newComb + result[idx] + " | ";
                    }
                }                                      
                newComb = newComb.Trim(new char[] { ' ', '|' });
                if (!result.ContainsValue(newComb) && !string.IsNullOrEmpty(newComb))
                {
                    result.Add(i, newComb);
                }                    
            }
        }
        return result;
    }

Upvotes: 0

M. Mimpen
M. Mimpen

Reputation: 1232

Since it's a flagged enum, why not simply:

  1. Get the highest vale of the enum.
  2. Calculate the amound of combinations, i.e. the upper bound.
  3. Iterate over every combination, i.e. loop from 0 to upper bound.

An example would look like this

var highestEnum = Enum.GetValues(typeof(MyEnum)).Cast<int>().Max();
var upperBound = highestEnum * 2;    
for (int i = 0; i < upperBound; i++)
{
    Console.WriteLine(((MyEnum)i).ToString());
}

Upvotes: 5

Aleksei
Aleksei

Reputation: 51

    public IEnumerable<TEnum> AllCombinations<TEnum>() where TEnum : struct
    {
        Type enumType = typeof (TEnum);
        if (!enumType.IsEnum)
            throw new ArgumentException(string.Format("The type {0} does not represent an enumeration.", enumType), "TEnum");

        if (enumType.GetCustomAttributes(typeof (FlagsAttribute), true).Length > 0) //Has Flags attribute
        {
            var allCombinations = new HashSet<TEnum>();

            var underlyingType = Enum.GetUnderlyingType(enumType);
            if (underlyingType == typeof (sbyte) || underlyingType == typeof (short) || underlyingType == typeof (int) || underlyingType == typeof (long))
            {
                long[] enumValues = Array.ConvertAll((TEnum[]) Enum.GetValues(enumType), value => Convert.ToInt64(value));
                for (int i = 0; i < enumValues.Length; i++)
                    FillCombinationsRecursive(enumValues[i], i + 1, enumValues, allCombinations);
            }
            else if (underlyingType == typeof (byte) || underlyingType == typeof (ushort) || underlyingType == typeof (uint) || underlyingType == typeof (ulong))
            {
                ulong[] enumValues = Array.ConvertAll((TEnum[]) Enum.GetValues(enumType), value => Convert.ToUInt64(value));
                for (int i = 0; i < enumValues.Length; i++)
                    FillCombinationsRecursive(enumValues[i], i + 1, enumValues, allCombinations);
            }
            return allCombinations;
        }
        //No Flags attribute
        return (TEnum[]) Enum.GetValues(enumType);
    }

    private void FillCombinationsRecursive<TEnum>(long combination, int start, long[] initialValues, HashSet<TEnum> combinations) where TEnum : struct
    {
        combinations.Add((TEnum)Enum.ToObject(typeof(TEnum), combination));
        if (combination == 0)
            return;

        for (int i = start; i < initialValues.Length; i++)
        {
            var nextCombination = combination | initialValues[i];
            FillCombinationsRecursive(nextCombination, i + 1, initialValues, combinations);
        }
    }

    private void FillCombinationsRecursive<TEnum>(ulong combination, int start, ulong[] initialValues, HashSet<TEnum> combinations) where TEnum : struct
    {
        combinations.Add((TEnum)Enum.ToObject(typeof(TEnum), combination));
        if (combination == 0)
            return;

        for (int i = start; i < initialValues.Length; i++)
        {
            var nextCombination = combination | initialValues[i];
            FillCombinationsRecursive(nextCombination, i + 1, initialValues, combinations);
        }
    }

Upvotes: 2

Greg
Greg

Reputation: 23463

Here is a solution particular to your code sample, using a simple for loop (don't use, see update below)

int max = (int)(MyEnum.Setting1 | MyEnum.Setting2 | MyEnum.Setting3 | MyEnum.Setting4);
for (int i = 0; i <= max; i++)
{
    var value = (MyEnum)i;
    SomeOtherFunction(value);
}

Update: Here is a generic method that will return all possible combinations. And thank @David Yaw for the idea to use a queue to build up every combination.

IEnumerable<T> AllCombinations<T>() where T : struct
{
    // Constuct a function for OR-ing together two enums
    Type type = typeof(T);
    var param1 = Expression.Parameter(type);
    var param2 = Expression.Parameter(type);
    var orFunction = Expression.Lambda<Func<T, T, T>>(
        Expression.Convert(
            Expression.Or(
                Expression.Convert(param1, type.GetEnumUnderlyingType()),
                Expression.Convert(param2, type.GetEnumUnderlyingType())),
            type), param1, param2).Compile();

    var initalValues = (T[])Enum.GetValues(type);
    var discoveredCombinations = new HashSet<T>(initalValues);
    var queue = new Queue<T>(initalValues);

    // Try OR-ing every inital value to each value in the queue
    while (queue.Count > 0)
    {
        T a = queue.Dequeue();
        foreach (T b in initalValues)
        {
            T combo = orFunction(a, b);
            if (discoveredCombinations.Add(combo))
                queue.Enqueue(combo);
        }
    }

    return discoveredCombinations;
}

Upvotes: 2

JBSnorro
JBSnorro

Reputation: 6706

I usually don't want to update each variable representing the max of an enumeration, when I add a new member to an enumeration. For example I dislike the statement Greg proposed:

int max = (int)(MyEnum.Setting1 | MyEnum.Setting2 | ... | MyEnum.SettingN);

Consider when you have several of these variabeles scattered throughout your solution and you decide to modify your enumeration. That surely isn't a desirable scenario.

I will admit in advance that my code is slower, but it is automatically correct after an enumeration has been modified, and I strive to code in such a robust manner. I'm willing to pay some computational penalty for that, C# is all about that anywayz. I propose:

public static IEnumerable<T> GetAllValues<T>() where T : struct
{
    if (!typeof(T).IsEnum) throw new ArgumentException("Generic argument is not an enumeration type");
    int maxEnumValue = (1 << Enum.GetValues(typeof(T)).Length) - 1;
    return Enumerable.Range(0, maxEnumValue).Cast<T>();
}

This assumes the enumeration contains members for all powers of 2 up to a certain power(including 0), exactly like a flag-enumeration is usually used.

Upvotes: 0

David Yaw
David Yaw

Reputation: 27864

First, grab a list of all the individual values. Since you've got 5 values, that's (1 << 5) = 32 combinations, so iterate from 1 to 31. (Don't start at zero, that would mean to include none of the enum values.) When iterating, examine the bits in the number, every one bit in the iteration variable means to include that enum value. Put the results into a HashSet, so that there aren't duplicates, since including the 'None' value doesn't change the resulting enum.

List<MyEnum> allValues = new List<MyEnum>(Enum.Getvalues(typeof(MyEnum)));
HashSet<MyEnum> allCombos = new Hashset<MyEnum>();

for(int i = 1; i < (1<<allValues.Count); i++)
{
    MyEnum working = (MyEnum)0;
    int index = 0;
    int checker = i;
    while(checker != 0)
    {
        if(checker & 0x01 == 0x01) working |= allValues[index];
        checker = checker >> 1;
        index++;
    }
    allCombos.Add(working);
}

Upvotes: 1

Related Questions