I m trying to average an array based on criteria in another array.
//array with a number of dates including hourly data
double[] dates;
//array with values, same length as dates and corresponding data points
double[] vals;
This is what I would like to do:
double[] dailyavgs = vals.GroupBy((v, i) => DateTime.FromOADate(dates[i]).Date()).Average().ToArray();
but this fails. Could you please point me in the right direction?
You can select an anonymous type and then use GroupBy:
double[] dailyavgs = vals
.Select((v, i) => new { Date = DateTime.FromOADate(dates[i]).Date, Value = v })
.GroupBy(x => x.Date)
.Select(g => g.Average(x => x.Value))
.ToArray();
Another similar approach using Enumerable.Zip:
double[] dailyavgs = vals
.Zip(dates, (v, d) => new { Date = DateTime.FromOADate(d).Date, Value = v })
.GroupBy(x => x.Date)
.Select(g => g.Average(x => x.Value))
.ToArray();
The latter has one advantage: it doesn't throw an exception if both arrays don't have the same size: " If the input sequences do not have the same number of elements, the method combines elements until it reaches the end of one of the sequences. For example, if one sequence has three elements and the other one has four, the result sequence has only three elements"
