Question

I am trying to figure out how to refactor this LINQ code nicely. This code and other similar code repeats within the same file as well as in other files. Sometime the data being manipulated is identical and sometimes the data changes and the logic remains the same.

Here is an example of duplicated logic operating on different fields of different objects.

public IEnumerable<FooDataItem> GetDataItemsByColor(IEnumerable<BarDto> dtos)
{
    double totalNumber = dtos.Where(x => x.Color != null).Sum(p => p.Number);
    return from stat in dtos
           where stat.Color != null
           group stat by stat.Color into gr
           orderby gr.Sum(p => p.Number) descending
           select new FooDataItem
           {
               Color = gr.Key,
               NumberTotal = gr.Sum(p => p.Number),
               NumberPercentage = gr.Sum(p => p.Number) / totalNumber
           };
}

public IEnumerable<FooDataItem> GetDataItemsByName(IEnumerable<BarDto> dtos)
{
    double totalData = dtos.Where(x => x.Name != null).Sum(v => v.Data);
    return from stat in dtos
           where stat.Name != null
           group stat by stat.Name into gr
           orderby gr.Sum(v => v.Data) descending
           select new FooDataItem
           {
               Name = gr.Key,
               DataTotal = gr.Sum(v => v.Data),
               DataPercentage = gr.Sum(v => v.Data) / totalData
           };
}

Anyone have a good way of refactoring this?

Answer 1

Something like this:

public IEnumerable<FooDataItem> GetDataItems<T>(IEnumerable<BarDto> dtos,
    Func<BarDto, T> groupCriteria,
    Func<BarDto, double> dataSelector,
    Func<T, double, double, FooDataItem> resultFactory)
{
    var validDtos = dtos.Where(d => groupCriteria(d) != null);
    double totalNumber = validDtos.Sum(dataSelector);

    return validDtos
        .GroupBy(groupCriteria)
        .OrderBy(g => g.Sum(dataSelector))
        .Select(gr => resultFactory(gr.Key,
                                    gr.Sum(dataSelector),
                                    gr.Sum(dataSelector) / totalNumber));
}

In your example, you might call it like this:

GetDataItems(
    x => x.Color,  // the grouping criterion
    x => x.Number, // the value criterion
    (key, total, pct) =>
        new FooDataItem {
            Color = key, NumberTotal = total, NumberPercentage = pct });

If you changed FooDataItem to be more generic, it would be easier.