Best collection to use with type Double as key

Question

I have this object:

Public Cactus{
    Public Double key;
    Public String value;
}

I have about ~100 Cactus, which all have

Answer 1

I agree with @Mark Byers and @tafa that using the double as the key directly is a bad idea. If you want to make sure that you have exactly the same number you could build a string key based on the bytes that make up the double. The following struct maps a double to the same memory space as 8 bytes so that no custom conversion is needed.

[StructLayout(LayoutKind.Explicit)]
public struct TestStruct
{
    [FieldOffset(0)]
    public byte byte1;
    [FieldOffset(1)]
    public byte byte2;
    [FieldOffset(2)]
    public byte byte3;
    [FieldOffset(3)]
    public byte byte4;
    [FieldOffset(4)]
    public byte byte5;
    [FieldOffset(5)]
    public byte byte6;
    [FieldOffset(6)]
    public byte byte7;
    [FieldOffset(7)]
    public byte byte8;

    [FieldOffset(0)]
    public double double1;
}

It can then wrapped in a function like this (assuming that you have the struct defined in your class as a private variable)

static string GetStringKey(double key)
{
    _conversionStruct.double1 = Double.MaxValue;

    return String.Format("{0}:{1}:{2}:{3}:{4}:{5}:{6}:{7}", 
        _conversionStruct.byte1,
        _conversionStruct.byte2, 
        _conversionStruct.byte3, 
        _conversionStruct.byte4, 
        _conversionStruct.byte5,
        _conversionStruct.byte6, 
        _conversionStruct.byte7, 
        _conversionStruct.byte8);
}

And used like this.

var s1 = GetStringKey(double.MaxValue);
var s2 = GetStringKey(double.MinValue);

which gives...

s1="255:255:255:255:255:255:239:127" 
s2="255:255:255:255:255:255:239:255"