Question

I have an arraylist of doubles returned by a JSON library. After the JSON parser’s decode method is run, we have this in the C# locals window:

Name     Value           Type
myObj    Count=4         object {System.Collections.ArrayList}
[0]      100.0           object {double}
[1]      244.0           object {double}
[2]      123.0           object {double}
[3]      999.0           object {double}

My goal is to produce an array of integers from this ArrayList. It would be simple to iterate and do this one value at a time, but I’d like to know how to do it using the built-in converter functionality. I have been reading theads on ConvertAll but I cannot get it to work.

I do not have control of the JSON library so I must begin with the ArrayList.

Thanks

Answer 1

You need to be careful with ArrayLists because of boxing. Thus:

// list is ArrayList      
int[] array = Array.ConvertAll(list.ToArray(), o => (int)(double)o);

Note the cast is framed as (int)(double). This first unboxes the boxed double and then casts to an int.

To do this in older versions of .NET

// list is ArrayList
int[] array = Array.ConvertAll(
    list.ToArray(),
    delegate(object o) { return (int)(double)o; }
);

An alternative is

// list is ArrayList
int[] array = Array.ConvertAll(
    (double[])list.ToArray(typeof(double)),
    o => (int)o
);

Here we do not need an unboxing operation because we have first converted the ArrayList to an array of unboxed doubles.

To do this in older versions of .NET

// list is ArrayList
int[] array = Array.ConvertAll(
    (double[])list.ToArray(typeof(double)),
    delegate(double o) { return (int)o; }
);