Question

I have the following method that takes an extremely long time to run and would love some help to make it run faster and or be more efficient.

The main responsibility of the method is to take a list of data points created from a CSV file, map the Name property of the file datapoints to the to the HistorianTagname property in a list of tagnames by the DataLoggerTagname property and create a resulting list from the mapping. If the mapping does not exist, the file datapoint is ignored.

I know it that was long-winded, but I hope it makes sense. It may be easier just to look at the method:

    private IEnumerable<DataPoint> GetHistorianDatapoints(IEnumerable<DataPoint> fileDatapoints, IEnumerable<Tagname> historianTagnames)
    {
        /**
         ** REFACTOR THIS 
         **/

        foreach (var fileDatapoint in fileDatapoints)
        {
            var historianTagname = historianTagnames.FirstOrDefault(x => x.DataLoggerTagname.Equals(fileDatapoint.Name, StringComparison.OrdinalIgnoreCase));
            if (historianTagname != null)
            {
                var historianDatapoint = new DataPoint();

                historianDatapoint.Name = historianTagname.HistorianTagname;
                historianDatapoint.Date = fileDatapoint.Date;
                historianDatapoint.Value = fileDatapoint.Value;

                yield return historianDatapoint;
            }
        }
    }

Notes:
I have complete control of classes and methods of mapping, so if I am doing something fundamentally wrong. I would love to know!

Thanks!

Answer 1

Below is my proposition:

private IEnumerable<DataPoint> GetHistorianDatapoints(IEnumerable<DataPoint> fileDatapoints, IEnumerable<Tagname> historianTagnames)
{
    var tagNameDictionary = historianTagnames.ToDictionary(t => t.DataLoggerTagname, StringComparer.OrdinalIgnoreCase);

    foreach (var fileDatapoint in fileDatapoints)
    {                
        if (tagNameDictionary.ContainsKey(fileDatapoint.Name))
        {
            var historianTagname = tagNameDictionary[fileDatapoint.Name];
            var historianDatapoint = new DataPoint();

            historianDatapoint.Name = historianTagname.HistorianTagname;
            historianDatapoint.Date = fileDatapoint.Date;
            historianDatapoint.Value = fileDatapoint.Value;

            yield return historianDatapoint;
        }
    }
}