I am looking for a way to look up values in a .net hash table using wildcards
I have a whole bunch of values stored in a .net 2.0 hash table. What I really would like to find is a way to essentially make a SQL select statement on a table.
Meaning, I would like to get a list of keys whose associated values match a very simple text pattern (along the lines "starts with a number".)
The ultimate goal will be to remove these records from the hash table for further processing.
I have already fought back a little from this, and I can not think of anything.
Any ideas?
(In case of coincidence, this matters: due to the realities of this project, any third-party widgets or updates to a later .net version are disconnected from the table.)
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You can use regex for every key in the hash table. It's very messy, but it works:
static void Main(string[] args)
{
Hashtable myhashtable = new Hashtable();
myhashtable.Add("Teststring", "Hello");
myhashtable.Add("1TestString1", "World");
myhashtable.Add("2TestString2", "Test");
List<String> newht = new List<String>;
//match all strings with a number at the front
Regex rx = new Regex("^[1-9]");
foreach (string key in myhashtable.Keys)
{
if (rx.IsMatch(key) == true)
{
newht.Add(key);
}
}
//Loop through all the keys in the new collection and remove them from
//them from the main hashtable.
foreach (string key in newht)
{
myhashtable.Remove(key);
}
}
EDIT: And just for fun, here's the LINQ version (sorry I'm just too).
Hashtable myhashtable = new Hashtable();
myhashtable.Add("Teststring", "Hello");
myhashtable.Add("1TestString1", "World");
myhashtable.Add("2TestString2", "Test");
Regex rx = new Regex("^[1-9]");
var k = (from string key in myhashtable.Keys
where rx.IsMatch(key)
select key).ToList();
k.ForEach(s => myhashtable.Remove(s));
EDIT: I just added a sting list, not a hash table, I couldn't remember which version of .net had shared lists in it. *** slaps thebhead
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If you are really looking for things that start with a number, then you can do it much faster than using Regex. Just look at the first character of each key and determine if it is a number. Save the keys that you want to remove in the list, as all you have to do is save the key.
List<string> keysToRemove = new List<string>( myhashtable.Count );
foreach (string key in myhashtable.Keys)
{
if (char.IsDigit(key[0])
{
keysToRemove.Add(key);
}
}
foreach (string key in keysToRemove)
{
myhashtable.Remove(key);
}
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Using LINQ:
Dim myhashtable As New Hashtable
myhashtable.Add("Teststring", "Hello")
myhashtable.Add("1TestString1", "World")
myhashtable.Add("2TestString2", "Test")
For Each i As String In From Element In myhashtable.Cast(Of DictionaryEntry)() Let k = DirectCast(Element.Value, String) Where k.StartsWith("W") Select DirectCast(Element.Key, String)
MsgBox("This key has a matching value:" & i)
Next
But it is better to use a dictionary if using LINQ:
Dim d = New Dictionary(Of String, String)()
d.Add("Teststring", "Hello")
d.Add("1TestString1", "World")
d.Add("2TestString2", "Test")
For Each i As String In From element In d Where element.Value.StartsWith("W") Select element.Key
MsgBox("This key has a matching value:" & i)
Next
And instead of .StartsWith ("W") you can of course do any other filtering you want.
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