Find the closest time from a list of times

Question

So, here's the scenario. I have a file with a created time, and I want to choose a time from a list of times that that file's created time is closest or equal too...what would be the best way to accomplish this?

Answer 1

get the difference of your file creatime and every time in your list and sort the absolute value of each time difference. the first one should be the answer you are looking for.

Answer 2

Use the minimum absolute time difference between the file time and the time in the list. You might get 2 entries being the same, and then you would need a different method to differ between these.

Answer 3

var creationTimes = new [] {DateTime.Now.AddDays(-1), DateTime.Now.AddDays(-2)};
FileInfo fi = new FileInfo("C:/test.xml");
var closestTime = creationTimes
    .OrderBy(c => Math.Abs(c.Subtract(fi.CreationTime).Days))
    .First();

Answer 4

Something like this:

DateTime fileDate, closestDate;
ArrayList theDates;
int min = int.MaxValue;

foreach (DateTime date in theDates)
 if (Math.Abs(date.Ticks- fileDate.Ticks) < min)
 {
   min = date.Ticks- fileDate.Ticks;
   closestDate = date;
 }

Answer 5

var min = listoftimes.Select(
    x => new { diff = Math.Abs((x - timeoffile).Ticks), time = x}).
    OrderBy(x => x.diff).
    First().time;

Note: Assumes at least 1 entry in listoftimes.

Answer 6

How often will you be doing this with the same list of times? If you're only doing it once, the fastest way is probably to just scan through the list and keep track of the closest time you've seen yet. When/if you encounter a time that's closer, replace the "closest" with that closer time.

If you're doing it very often, you'd probably want to sort the list, then use a binary search.

Answer 7

var closestTime = listOfTimes
                  .OrderBy(t => Math.Abs((t - fileCreateTime).Ticks))
                  .First();

If you don't want the performance overhead of the OrderBy call then you could use something like the MinBy extension method from MoreLINQ instead:

var closestTime = listOfTimes
                  .MinBy(t => Math.Abs((t - fileCreateTime).Ticks));

Answer 8

var closestTime = (from t in listOfTimes
                   orderby (t - fileInfo.CreationTime).Duration()
                   select t).First();

Answer 9

Not an answer, but a question regarding the various LINQ solutions proposed above. How efficient is LINQ? I have not written any "real" programs with LINQ yet, so I'm not sure on the performance.

In this example, the "listOfTimes" collection implies that we have already iterated over some file system based objects to gather the times. Would it have been more efficient to do the analysis during the iteration instead of later in LINQ? I recognize that these solutions may be more "elegant" or nicely abstract the "collection as database" idea, but I tend to choose efficiency (must be readable though) over elagance in my programming. Just wondering if the cost of LINQ might outweigh the elegance here?

Answer 10

The accepted answer is completely wrong. What you want is something like this:

  DateTime fileDate, closestDate;
  List<DateTime> theDates;

  fileDate = DateTime.Today;       //set to the file date
  theDates = new List<DateTime>(); //load the date list, obviously

  long min = Math.Abs(fileDate.Ticks - theDates[0].Ticks);
  long diff;
  foreach (DateTime date in theDates)
  {
    diff = Math.Abs(fileDate.Ticks - date.Ticks);
    if (diff < min)
    {
      min = diff;
      closestDate = date;
    }
  }