How to pass property and sortorder as parameters for sorting list in method

Question

I have a method where I pass in a List, which is then sorted in the method.

The type ChartItemData includes properties like Average, ProportionHighScore, and ProportionLowScore. Depending on method usage, I need to sort the List inside the method on different properties, and either Ascending or Descending.

How can I specify in the parameter list of the method which property to sort on, and which sortorder to use?

I imagine I could set up an Enum for SortDirection, but I still need to find out how to pass in the property to sort on. Here is some pseudocode to illustrate what I'm after, using List.OrderBy. I could also sort the List in place with the List.Sort method, if that makes more sense.

public enum SortDirection { Ascending, Descending }

public void myMethod(List<ChartItemData> myList, "parameter propertyToSortOn", 
    SortDirection direction)
{
     if (direction == SortDirection.Ascending)
        var sorted = ChartData.OrderBy(x => x."propertyToSortOn").ToList();
     else
        var sorted = ChartData.OrderByDescending(x => x."propertyToSortOn").ToList();
}

Try using reflection to get the correct property based on the string passed in: msdn.microsoft.com/en-us/library/kz0a8sxy(v=vs.110).aspx — John Bustos
– John Bustos, Commented Mar 2, 2016 at 20:45
You can define your own comparer, see this link : stackoverflow.com/questions/12753762/… — Aliz
– Aliz, Commented Mar 2, 2016 at 20:47

Evert · Accepted Answer · 2016-03-02 20:50:09Z

2

Would something like this work? It allows you to refer to the property to sort on through the second method parameter (a lambda). Otherwise you'd be pretty much stuck to reflection.

public class ChartItemData
    {
        public double Average { get; set; }
        public double HighScore { get; set; }
        public double LowScore { get; set; }

        public string Name { get; set; }
    }

    class Program
    {
        public enum SortDirection { Ascending, Descending }

        public void myMethod<T>(List<ChartItemData> myList, Func<ChartItemData, T> selector, SortDirection direction)
        {
            List<ChartItemData> sorted = null;

            if (direction == SortDirection.Ascending)
            {
                sorted = myList.OrderBy(selector).ToList();
            }
            else
            {
                sorted = myList.OrderByDescending(selector).ToList();
            }

            myList.Clear();
            myList.AddRange(sorted);
        }

        public void usage()
        {
            List<ChartItemData> items = new List<ChartItemData>();

            myMethod(items, x => x.Average, SortDirection.Ascending);
            myMethod(items, x => x.Name, SortDirection.Ascending);
        }

answered Mar 2, 2016 at 20:50

Evert

3542 silver badges8 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Proposition Joe Over a year ago

Thanks, this looks good - and also nice that I got to try out and understand the "Method<T>" signature, which I haven't used before.

John Bustos · Accepted Answer · 2016-03-02 20:53:30Z

1

I'd say the easiest way would be to use reflection to get the PropertyInfo from the name provided.

You can then use that PropertyInfo to get the value from each value within the list to sort the list in the following way:

public List<ChartItemData> myMethod(List<ChartItemData> myList, string propName, SortDirection direction)
{
    var desiredProperty = typeof(ChartItemData).GetProperty(propName, BindingFlags.Public | BindingFlags.Instance);

    if (direction == SortDirection.Ascending)
        return myList.OrderBy(x => desiredProperty.GetValue(x)).ToList();
    else
        return myList.OrderByDescending(x => desiredProperty.GetValue(x)).ToList();
}

answered Mar 2, 2016 at 20:53

John Bustos

19.7k18 gold badges102 silver badges162 bronze badges

1 Comment

Proposition Joe Over a year ago

Very nice, this would work. I'll try it out in some scenarios. However, if I understand correctly, here I need to pass the property name as hardcoded, so presumably if I change property names I have to then also update the string code? I assume there's no Object.Property.PropertyNameToString()?

Collectives™ on Stack Overflow

How to pass property and sortorder as parameters for sorting list in method

2 Answers 2

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related