Refactoring blocks of code that differ only by one function call

Question

I've got similar formulas for counting Hartley transformation. The only difference is input function - sin, cos, exp in the following lines of code:

Math.Exp((double)tau)
Math.Sin((double)tau)
Math.Cos((double)tau)

How can I escape almost identical code fragments and shorten my code in following fragment?

 private void CountHartley(ref double [] arr, string function)
        {
            int N = arr.Length;
            if (function == "exp")
            {
                for (int nu = 0, tau = 0; ((nu < N) && (tau < N)); nu++, tau++)
                {
                    arr[nu] = 1 / (double)N *
                                 Math.Exp((double)tau) *
                                 (Math.Sin(2 * Math.PI * nu * tau / (double) N) +
                                 Math.Cos(2 * Math.PI * nu * tau / (double) N));
                }
            }
            else if (function == "sin")
            {
                for (int nu = 0, tau = 0; ((nu < N) && (tau < N)); nu++, tau++)
                {
                    arr[nu] = 1 / (double)N *
                                 Math.Sin((double)tau) *
                                 (Math.Sin(2 * Math.PI * nu * tau / (double)N) +
                                 Math.Cos(2 * Math.PI * nu * tau / (double)N));
                }
            }
            else
            {
                for (int nu = 0, tau = 0; ((nu < N) && (tau < N)); nu++, tau++)
                {
                    arr[nu] = 1 / (double)N *
                                 Math.Cos((double)tau) *
                                 (Math.Sin(2 * Math.PI * nu * tau / (double)N) +
                                 Math.Cos(2 * Math.PI * nu * tau / (double)N));
                }
            }
}

dtb · Accepted Answer · 2012-04-28 14:52:40Z

6

Instead of passing in a string with the function to use, you can pass in the function directly.

You can use the Func<T, TResult> Delegate for this as follows:

private void CountHartley(ref double [] arr, Func<double, double> function)
{
    int N = arr.Length;
    for (int nu = 0, tau = 0; ((nu < N) && (tau < N)); nu++, tau++)
    {
        arr[nu] = 1 / (double)N *
                     function((double)tau) *
                     (Math.Sin(2 * Math.PI * nu * tau / (double) N) +
                     Math.Cos(2 * Math.PI * nu * tau / (double) N));
    }
}

Usage:

var result = CountHartley(arr, Math.Cos);

answered Apr 28, 2012 at 14:52

dtb

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2 Comments

user703016 Over a year ago

The casts to double could probably be removed (and N declared as double too).

dtb Over a year ago

ref is also not needed, and nu and tau seem to be always the same. So the code could indeed be refactored a bit. But I'll leave it intact so the OP can more easily spot the difference to his/her own code.

Jason Kleban · Accepted Answer · 2012-04-28 14:54:17Z

0

How about passing in the Math.* as an argument to a Func<double, double> function parameter?

answered Apr 28, 2012 at 14:54

Jason Kleban

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