C# List<List<string>> filtering with LinQ

Question

I have a List<List<string>> and need to filter the inner List. It looks like this:

{["/DownloadFile2.aspx?File=1026704PR20131001.PDF","10/1/2013 | Monthly Memo","10/1/2013","","","CI","","","","","",""],
 ["/DownloadFile2.aspx?File=1026704PR20141001.PDF","10/1/2014 | Monthly Memo","10/1/2014","","","CC","","","","","",""],
 ["/DownloadFile2.aspx?File=1026704date20130928.PDF","9/30/2013 | New Memo","9/30/2013","","","CC","","","","","",""],
 ["/DownloadFile2.aspx?File=1026704date20140928.PDF","9/30/2014 | New Memo","9/30/2014","","","CI","","","","","",""]}

How would I filter the second column using a LINQ .Where clause?

Like filtering on the term "Monthly" would return:

{["/DownloadFile2.aspx?File=1026704PR20131001.PDF","10/1/2013 | Monthly Memo","10/1/2013","","","CI","","","","","",""],
 ["/DownloadFile2.aspx?File=1026704PR20141001.PDF","10/1/2014 | Monthly Memo","10/1/2014","","","CC","","","","","",""]}

Adding Code

Archive Definition from my web service:

[DataContract(Namespace = "http://www.mysite.com")]
public class Archive
{
    [DataMember]
    public List<string> Header {get; set;}

    [DataMember]
    public List<List<string>> Rows{get; set;}
}

Code geting the Archive from the service (mps is the web service)

/// param contains values used to retrieve a partial set
/// as well as other values used to pass data to jQuery DataTable
///
Archive docs = mps.GetArchiveArray(LogonTicket, PID, param.iDisplayStart, param.iDisplayLength, "D");

List<List<string>> filteredRows;

// If the params sSearch value is not null or empty, filter the results
// else return the full results
if (!string.IsNullOrEmpty(param.sSearch))
{
    // Here's where I need to filter the result set based on the params.sSeach value.
    filteredRows = docs.Rows.?????;
}
else
{
    filteredRows = docs.Rows;
}

The filteredRows are then passed through a loop to build my JSON using a StringBuilder and then the full desired result is sent as JSON:

string result =  sb.ToString();
return Json(new
{
    sEcho = param.sEcho,
    iTotalRecords = numDocs,
    iTotalDisplayRecords = numDocs,
    aaData = result
},
JsonRequestBehavior.AllowGet);

Chris Ballard · Accepted Answer · 2014-03-20 20:12:01Z

3

Use the Select clause on the outer list, so something like:

outerList.Select(inr => inr.Where(...))

answered Mar 20, 2014 at 20:12

Chris Ballard

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3 Comments

MB34 Over a year ago

filteredRows = Rows.Select(inr => inr.Where(inr[1].Contains(param.sSearch))); produces

'System.Collections.Generic.List<string>' does not contain a definition for 'Where' and the best extension method overload 'System.Linq.Enumerable.Where<TSource>(System.Collections.Generic.IEnumerable<TSource>, System.Func<TSource,int,bool>)' has some invalid arguments

bnem Over a year ago

@MB34, the where requires a Func<T, bool> parameter, typically in the form of a lambda expression. Your statement should be written as filterRows = Rows.Select(inr => inr.Where(x => x[1].Contains(...)));

MB34 Over a year ago

filteredRows = Docs.Rows.Select(inr => inr.Where(x => x[1].Contains(param.sSearch))); shows error "'char' does not contain a definition for 'Contains'". Besides, isn't using x[1] searching only the second column?

Lasse Espeholt · Accepted Answer · 2014-04-02 18:14:01Z

3

var lists = ...;
var filteredLists = (from list in lists
                     where list[1].EndsWith(" | Monthly Memo")
                     select list).ToList();

Or if it is only that it contains Monthly then

var lists = ...;
var filteredLists = (from list in lists
                     where list[1].Contains("Monthly")
                     select list).ToList();

Or lower/upper case doesn't matter then

var lists = ...;
var filteredLists = (from list in lists
                     where list[1].ToLower().Contains("monthly")
                     select list).ToList();

When introducing ToList the lambda syntax may be clearer:

var filteredLists = lists.Where(list => list[1].Contains("Monthly"))
                         .ToList()

EDIT If you want to check all columns:

var filteredLists = lists.Where(list => list.Any(s => s.Contains("Monthly")))
                         .ToList()

edited Apr 2, 2014 at 18:14

answered Mar 20, 2014 at 20:12

Lasse Espeholt

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7 Comments

MB34 Over a year ago

See above, however, it should have been fairly evident.

Lasse Espeholt Over a year ago

And what result did you get? What "didn't work" for you?

MB34 Over a year ago

Both showed this error:

Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<System.Collections.Generic.List<string>>' to 'System.Collections.Generic.List<System.Collections.Generic.List<string>>'. An explicit conversion exists (are you missing a cast?)

when called like this: filteredRows = from list in docs.Rows where list[1].Contains("Monthly") select list;

MB34 Over a year ago

I cannot just search the second column, that's what the list[1] is, correct? I need to search all columns.

Lasse Espeholt Over a year ago

See updated answer. Next time you ask a question, try to be more precise or provide more examples.

|

bnem · Accepted Answer · 2014-03-20 20:47:19Z

0

Use this (it works):

var listsWithMonthly = listOfLists.Where(x => x.Any(subx => subx.Contains("Monthly"))).ToList();

For filtering just on the second column in the inner list, this works too:

var listsWithMonthly = listOfLists.Where(x => x[1].Contains("Monthly")).ToList();

edited Mar 20, 2014 at 20:47

answered Mar 20, 2014 at 20:25

bnem

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8 Comments

default Over a year ago

I first thought if this as well, but it seems that the OP wants the result to be the complete list and not just that one string element. This will select just the strings that contains Monthly, not the whole lists.

MB34 Over a year ago

How to make the first one case-insensitive?

bnem Over a year ago

@MB34 var listsWithMonthly = listOfLists.Where(x => x.Any(subx => subx.ToLower().Contains("monthly"))).ToList(); should work

MB34 Over a year ago

I thought I already tried that. Anyway Here's results: System.NullReferenceException was unhandled by user code Message=Object reference not set to an instance of an object. On this line: filteredRows = docs.Rows.Where(x => x.Any(subx => subx.ToLower().Contains(param.sSearch))).ToList(); Apparently subx is null.

bnem Over a year ago

Then you would do something like this: filteredRows = docs.Rows.Where(x => x.Any(subx => (subx ?? string.Empty).ToLower().Contains(param.sSearch))).ToList();. Defaulting the string to string.Empty if it is null ??, will avoid the exception.

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