创建通用函数以在C＃中将数组转换为字典

Question

I have a struct which contains two public variables. I have made an array of that struct, and wish to convert it to a Dictionary.

Here is one such method of accomplishing that:

public class TestClass
{
    public struct KeyValuePairs
    {
        public string variableOne;
        public float variableTwo
    }

    private KeyValuePairs[] keyValuePairs;

    private Dictionary<string, float> KeyValuePairsToDictionary()
    {
        Dictionary<string, float> dictionary = new Dictionary<string, float>();

        for(int i = 0; i < keyValuePairs.Length; i++)
        {
            dictionary.Add(keyValuePairs[i].variableOne, keyValuePairs[i].variableTwo);
        }

        return dictionary;
    }
}

Now, that works for my specific setup, but I wish to try and convert the KeyValuePairsToDictionary() function into a Generic so that it may work across all types.

My first thought, then, was to do something like this:

private Dictionary<T, T> ArrayToDictionary<T>(T[] array)
{
    Dictionary<T, T> keyValuePairs = new Dictionary<T, T>();

    for(int i = 0; i < array.Length; i++)
    {
        keyValuePairs.Add(array[i], array[i]); //The problem is right here.
    }

    return keyValuePairs;
}

As you can probably tell, I can't access the public fields of whatever struct array I am trying to convert into key-value pairs.

With that, how would you suggest I go about performing the generic conversion?

Please note that my specific setup requires that I convert a struct to a dictionary, for I am using the Unity Game Engine.

Thank you.

Answer 1

A generic way of doing this is already implemented in LINQ.

var dict = myArray.ToDictionary(a => a.TheKey);

---

With your implementation

public struct KeyValuePairs
{
    public string variableOne;
    public float variableTwo;
}

and an array

KeyValuePairs[] keyValuePairs = ...;

You get

Dictionary<string, KeyValuePairs> dict = keyValuePairs
    .ToDictionary(a => a.variableOne);

or alternatively

Dictionary<string, float> dict = keyValuePairs
    .ToDictionary(a => a.variableOne, a => a.variableTwo);

Note that the first variant yields a dictionary with values of type KeyValuePairs , while the second one yields values of type float .

---

According to the conversation, it seems that you are interested on how you would implement this. Here is a suggestion:

public static Dictionary<TKey, TValue> ToDictionary<T, TKey, TValue>(
    this IEnumerable<T> source,
    Func<T, TKey> getKey,
    Func<T, TValue> getValue)
{
    var dict = new Dictionary<TKey, TValue>();
    foreach (T item in source) {
        dict.Add(getKey(item), getValue(item));
    }
    return dict;
}

Or simply like this, if you want to store the item itself as value

public static Dictionary<TKey, T> ToDictionary<T, TKey>(
    this IEnumerable<T> source,
    Func<T, TKey> getKey
{
    var dict = new Dictionary<TKey, T>();
    foreach (T item in source) {
        dict.Add(getKey(item), item);
    }
    return dict;
}

Answer 2

You can use Reflection to achieve that

First of all, add a {get;set;} to the variables to transform them in properties

public struct KeyValuePairs
{
    public string variableOne { get; set; }
    public float variableTwo { get; set; }
}

Then the method

// T1 -> Type of variableOne
// T2 -> Type of variableTwo
// T3 -> KeyValuesPair type
public static Dictionary<T1, T2> convert<T1,T2,T3>(T3[] data)
{
    // Instantiate dictionary to return
    Dictionary<T1, T2> dict = new Dictionary<T1, T2>();

    // Run through array
    for (var i = 0;i < data.Length;i++)
    {
        // Get 'key' value via Reflection to variableOne
        var key = data[i].GetType().GetProperty("variableOne").GetValue(data[i], null);
        // Get 'value' value via Reflection to variableTow
        var value = data[i].GetType().GetProperty("variableTwo").GetValue(data[i], null);
        // Add 'key' and 'value' to dictionary casting to properly type
        dict.Add((T1)key, (T2)value);
    }
    //return dictionary
    return dict;
}

I used the following code to test

KeyValuePairs[] val = new KeyValuePairs[5];

val[0] = new KeyValuePairs() { variableOne = "a", variableTwo = 2.4f };
val[1] = new KeyValuePairs() { variableOne = "b", variableTwo = 3.5f };
val[2] = new KeyValuePairs() { variableOne = "c", variableTwo = 4.6f };
val[3] = new KeyValuePairs() { variableOne = "d", variableTwo = 5.7f };
val[4] = new KeyValuePairs() { variableOne = "e", variableTwo = 6.8f };

Dictionary<string, float> dict = convert<string, float,KeyValuePairs>(val);