how to remove empty strings from list then remove duplicate values from a list

Question

Lets say I have a list of some column values coming from a table  how do I remove empty strings and duplicate values  Please see the following code   List lt string gt  dtList   dtReportsList AsEnumerable   Select dr   gt  dr Field lt string gt   column1    ToList      This is what I have coded just now but but Amiram s code is way more elegant  so I will choose  that answer here is how I did it   DataTable dtReportsList   someclass GetReportsList             if  dtReportsList Rows Count  gt  0                       List lt string gt  dtList   dtReportsList AsEnumerable   Select dr   gt  dr Field lt string gt   column1    ToList               dtList RemoveAll x  gt x                    dtList   dtList Distinct   ToList                         rcboModule DataSource   dtList             rcboModule DataBind                              rcboModule Items Insert 0  new RadComboBoxItem  All    All

User · Answer

Amiram Korach solution is indeed tidy  Here s an alternative for the sake of versatility   var count   dtList Count     Perform a reverse tracking  for  var i   count - 1  i  gt  -1  i--        if  dtList i   string Empty  dtList RemoveAt i        Keep only the unique list items  dtList   dtList Distinct   ToList

User · Answer

Amiram s answer is correct  but Distinct   as implemented is an N2 operation  for each item in the list  the algorithm compares it to all the already processed elements  and returns it if it s unique or ignores it if not  We can do better   A sorted list can be deduped in linear time  if the current element equals the previous element  ignore it  otherwise return it  Sorting is NlogN  so even having to sort the collection  we get some benefit   public static IEnumerable lt T gt  SortAndDedupe lt T gt  this IEnumerable lt T gt  input       var toDedupe   input OrderBy x  gt x       T prev     foreach var element in toDedupe             if element    prev  continue         yield return element        prev   element                  Usage dtList    dtList Where s   gt   string IsNullOrWhitespace s   SortAndDedupe   ToList      This returns the same elements  they re just sorted

User · Answer

To simplify Amiram Korach s solution  dtList RemoveAll s   gt  string IsNullOrWhiteSpace s    No need to use Distinct   or ToList

User · Answer

dtList    dtList Where s   gt   string IsNullOrWhiteSpace s   Distinct   ToList     I assumed empty string and whitespace are like null  If not you can use IsNullOrEmpty  allow whitespace   or s    null

[c#] how to remove empty strings from list, then remove duplicate values from a list

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