Question

I have a datatable that has many fields from many event files. I need to be able to select distinct on the time. The datetime field is in this format MM/dd/yyyy HH:mm:ss .. I am trying this:

dpall = RollUpValuesFunctions.jobTableFinalCSVOutput.DefaultView.ToTable();

what I am wondering is if there is a way to apply a constraint on the datetime field to only get a distinct date like MM/dd/yyyy HH:mm?
Each minute has a couple hundred records, but for my purposes I only need one of the records from that minute.

And this is in C#

Answer 1

Given the following data:

var dt = new DataTable();
dt.Columns.Add(new DataColumn("Time", typeof(DateTime)));
dt.Rows.Add(new DateTime(2000, 12, 31, 12, 0, 0));
dt.Rows.Add(new DateTime(2000, 12, 31, 12, 0, 0));
dt.Rows.Add(new DateTime(2000, 12, 31, 12, 0, 1));
dt.Rows.Add(new DateTime(2000, 12, 31, 12, 0, 2));
dt.Rows.Add(new DateTime(2000, 12, 31, 12, 4, 2));
dt.Rows.Add(new DateTime(2000, 12, 31, 12, 5, 5));
dt.Rows.Add(new DateTime(2000, 12, 31, 12, 5, 2));

the obvoius Linq approach is

var result = from row in dt.AsEnumerable()
             let d = row.Field<DateTime>("Time")
             group row by new DateTime(d.Year, d.Month, d.Day, d.Hour, d.Minute, 0) into g
             select g.First();

foreach (DataRow row in result)
    Console.WriteLine(row["Time"]);   

but since you asked for a non-linq solution, why not just iterate over each row, get rid of the seconds part of the time, and use a DataView to do the Distinct part:

foreach (DataRow row in dt.Rows)
{
    DateTime d = row.Field<DateTime>("Time");
    row["Time"] = new DateTime(d.Year, d.Month, d.Day, d.Hour, d.Minute, 0);
    // or use "tricks" like this
    // row["Time"] = d.AddTicks(-(d.Ticks % TimeSpan.TicksPerMinute));
}

foreach(DataRow r in new DataView(dt).ToTable(true).Rows)
    Console.WriteLine(r["Time"]);

If you don’t want to change your DataTable, you can copy it before.