I have a List<string> with dates.
My list is:
{"01/01/2013","10/01/2013","20/01/2013"}
I want to sort the list to look like this:
{"20/01/2013","10/01/2013","01/01/2013"}
How can I make this?
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6 Answers
With linq:
var list = new List<string> {"01/01/2013", "10/01/2013", "20/01/2013"};
var orderedList = list.OrderByDescending(x => DateTime.Parse(x)).ToList();
UPDATE (according questions in comments):
You can treat invalid dates like this (invalid date is there treated as default(DateTime)):
var list = new List<string> { "01/01/2013", "10/01/2013", "N/A" , "20/01/2013" };
var orderedList2 = list.OrderByDescending(x =>
{
DateTime dt;
DateTime.TryParse(x, out dt);
return dt;
});
Or if you want to have invalid datetime as first item in the list:
var orderedList3 = list.OrderByDescending(x =>
{
DateTime dt;
if (!DateTime.TryParse(x, out dt)) return DateTime.MaxValue;
return dt;
});
You can also filter the invalid dates out:
var filteredList = list.Where(x =>
{
DateTime dt;
return DateTime.TryParse(x, out dt);
}).Select(DateTime.Parse).OrderByDescending(x => x);
Or even better:
var filteredList = list.Select(x =>
{
DateTime dt;
return new {valid = DateTime.TryParse(x, out dt), date = dt};
}).Where(x => x.valid).Select(x => x.date).OrderByDescending(x => x);
2 Comments
Yusril Maulidan Raji
How about if there is an invalid datetime string? Is there any way to alter that invalid datetime with a specific string?
Demodave
What if there are strings as well? Like missing? how do you sort
You shouldn't use string representations of data - we're all living in object-oriented world :)
Best way would be to convert these strings into actual DateTime objects and sort them in reverse order via linq:
var dates = Array.ConvertAll(dateStrings, x => DateTime.Parse(x));
return dates.OrderByDesc(x => x);
Another way would be to implement custom sorting function, see this link. Then you'd just use it in a sort function:
DateAsStringComparer myComparer = new DateAsStringComparer();
dateStrings.Sort(myComparer);
2 Comments
Simon Whitehead
+1 because you didn't bother with the string comparison like I did :)
himanshupareek66
actually, you don't need the lambda, you can do it like this -Array.ConvertAll(dateStrings,DateTime.Parse)
Try this:
List<string> s = new List<string>() { "01/01/2013", "10/01/2013", "20/01/2013" };
var d = s.OrderByDescending(i => DateTime.ParseExact(i, "dd/MM/yyyy", null));
Comments
Why do you want to use List<string> instead of List<DateTime>?
List<DateTime> dates = ...
dates.OrderByDescending(c => c).ToList();
1 Comment
Martin K
I'm sure he had his reasons. I need it as well, for example.
Because they are the UK/AUS format (Day/Month/Year), you can sort them using OrderByDescending:
List<string> dates = new List<string>() { "01/01/2013", "10/01/2013", "20/10/2013" };
foreach (var date in dates.OrderByDescending(x => x))
Console.WriteLine(date);
Personally I would convert them to DateTime objects first..
Comments
To convert DateTime string of custom format to string of unified format, you can adopt following simple and safe snippet.
string formatStr = "yyyyMMddHHmmss";
string result = Convert.ToDateTime(inputStr).ToString(formatStr);
Inside the code, formatStr can be any possible forms the DateTime class can accept, you can set it as the format you need, here you can just use dd/MM/yyyy which is matched with your target format string such as "20/01/2013".
So for your case, the code can be simple as below:
List<string> list = new List<string> { "01/01/2013", "10/01/2013", "20/01/2013" };
var listAfterSorting = list.OrderByDescending(t =>
Convert.ToDateTime(t).ToString("dd/MM/yyyy")
.ToList());
While in some cases, using ParseExact to parse a data time string, it will throws error/exception String was not recognized as a valid DateTime, in that case if you turn to use TryParseExact, the result is probably default(DateTime)= 1/1/0001 12:00:00 AM because of parsing failed. Therefore, I do not recommend ParseExact or TryParseExact.
