如何将从此Linq查询中检索到的值检查为.ToLower（）？

Question

This is my code:

DataRow r = VirtualTable
  .AsEnumerable()
  .FirstOrDefault(tt => (tt.Field<string>("Column1") == value1) ||
                        (tt.Field<string>("Column1") == value2));

This code retrieves a data row whose 'Column1' matches a given string. I then check this against a bool if statement. However, though I can change my string's capitalization, I don't know how to handle it with the value Linq gives me. Still learning linq, so I don't know my way around it yet.

In short, I have the string "Red box" in the table, but want it to be read as "red box" so it will match my internal string of the same value.

Additionally, I was trying to retrieve the IndexOf the row this query gives me, but I'm always retrieving a -1 even if it finds a match.

Here's the code to retrieve it:

int SelectedIndex = VirtualTable.Rows.IndexOf(r);

Answer 1

Try string.Equals to ignore case and overload Select to get row's index:

   var row = VirtualTable
     .AsEnumerable()
     .Select((tt, index) => new {
        value = tt.Field<string>("Column1"),
        index = index})
     .FirstOrDefault(item => 
        string.Equals(item.value, value1, StringComparison.OrdinalIgnoreCase) ||
        string.Equals(item.value, value2, StringComparison.OrdinalIgnoreCase));

   // If we have the row found, we can get
   if (row != null) {
     var r = row.value;              // value, e.g. "bla-bla-bla"
     int selectedIndex = row.index;  // as well as its index, e.g. 123 
     ... 
   }

Answer 2

You can use String.Equals(string,StringComparisonOption) to compare two strings using case-insensitive comparison. This avoids generating yet-another-temporary-string as ToLower() would do, eg:

tt.Field<string>("Column1").Equals(value1,StringComparison.OrdinalIgnoreCase)

or

tt.Field<string>("Column1").Equals(value1,StringComparison.CurrentCultureIgnoreCase)

Make sure you use the appropriate comparison option. Different cultures have different casing rules. Ordinal is the fastest option as it compares strings using binary rules.