How do I implement an unknown Array type in C# .Net Core?-CodePudding

I have the following code below but haven't figured out how to implement the var results = section so that result[c] = valuesArray; works properly?

    var result = Array.CreateInstance(typeof(Array), dt.Columns.Count);

            foreach (int c in Enumerable.Range(0, dt.Columns.Count))
            {
                // Create a list to hold values of the required type for the column
                var valuesArray = Array.CreateInstance(typeof(float), dt.Rows.Count);

                // Get the data to be written to the parquet stream
                for (int r = 0; r < dt.Rows.Count; r  )
                {
                    DataRow row = dt.Rows[r];

                    valuesArray.SetValue(row[c], r);
                }

                result[c] = valuesArray;

The error is:

Error: CS0021 = Cannot apply indexing with [] to an expression of type 'Array'

How do I instiate the Array so it works?

CodePudding user response：

Just as you set a value to valuesArray with the SetValue() method, you can do the same for result:

result.SetValue(valuesArray, c);

If you need to retrieve the value during iteration, you can use result.GetValue(c):

foreach (int c in result)
{
    var retrievedResult = result.GetValue(c);
}

CodePudding user response：

The Nice approach that I've tried and works correctly is:

 var result = (dynamic)Array.CreateInstance(typeof(Array), columnLength);

The sample code is:

int columnLength = 8;
var result = (dynamic)Array.CreateInstance(typeof(Array), columnLength);

foreach (int c in Enumerable.Range(0, columnLength)) {
    // Create a list to hold values of the required type for the column
    var valuesArray = Array.CreateInstance(typeof(float),columnLength);

    // Get the data to be written to the parquet stream
    for (int r = 0; r < columnLength; r  ) {

        valuesArray.SetValue(r, r);
    }

    result[c] = valuesArray;
}

foreach (var arr in result)
    foreach (var value in arr)
        Console.Write($"{value}\t");
Console.ReadLine();

The Output is:

0       1       2       3       4       5       6       7       0       1       2       3       4       5       6
        7       0       1       2       3       4       5       6       7       0       1       2       3       4
        5       6       7       0       1       2       3       4       5       6       7       0       1       2
        3       4       5       6       7       0       1       2       3       4       5       6       7       0
        1       2       3       4       5       6       7

CodePudding user response：

It looks like result.SetValue(valuesArray, c) will work.

You can also get the value with

result.GetValue(c);

So if you need to iterate through result you can write a foreach similar to the one you already wrote.

foreach (int c in Enumerable.Range(0, dt.Columns.Count))
{
   var x = result.GetValue(c);
}

CodePudding user response：

You can utilize generics for this. The only reflection you need is to execute the inner function once per column.

The initial array of arrays can be done without Array.CreateInstance

var method = this.GetType().GetMethod("GetArray");

var result = new Array[dt.Columns.Count];

for (int c = 0; c < dt.Columns.Count; c  )
{
    var generic = method.MakeGenericMethod(dt.Columns[c].DataType);
    result[c] = (Array)generic.Invoke(null, new[]{dt.Rows, c});
}

public static Array GetArray<T>(DataRowCollection rows, int c)
{
    var valuesArray = new T[rows.Count];
    for (int r = 0; r < rows.Count; r  )
    {
        DataRow row = rows[r];
        valuesArray[r] = (T)row[c];
    }
    return valuesArray;
}

In high performance scenarios, you could even cache a delegate to the generic function

static MethodInfo method = this.GetType().GetMethod("GetArray");

static Dictionary<Type, Func<DataRowCollection, int, Array>> funcs = new();

var result = new Array[dt.Columns.Count];

for (int c = 0; c < dt.Columns.Count; c  )
{
    if(!funcs.TryGetValue(dt.Columns[c].DataType, out var func)
    {
        func = funcs[dt.Columns[c].DataType] =
          (Func<DataRowCollection, int, Array>) method.MakeGenericMethod(dt.Columns[c].DataType)
             .CreateDelegate(typeof(Func<DataRowCollection, int, Array>));
    }
    result[c] = func(dt.Rows, c);
}