I am using following code:
var names = ConfigurationManager.AppSettings.AllKeys.Where(k => k.StartsWith("name"));
and i get keys like: name1, name2, name16, name18.
Now i want to create another array which will remove name and just keep 1,2,16,18. Is there any easy way to do this in above code itself? Or do it seperatly?
You can directly
ConfigurationManager.AppSettings.AllKeys.Where(k => k.StartsWith("name")).Select(a => a.Replace("name",""));
static Replace method, so it won't compile, I guess. It's bad to call ToList() before the Select (in the second code line).
SubString is a much better approach as you know your text starts with your search string from the thanks to the Where clause.I think your code is good enough. Just a little bit of performance improve by using substring as it's straightforward operation to remove prefix:
var prefix = "name"; // could be a parameter or used as const; just for example
var nums = ConfigurationManager.AppSettings.AllKeys.Where(s => s.StartsWith(prefix)).Select(s => s.Substring(prefix.Length)).ToArray();
Try this:
var names = ConfigurationManager.AppSettings.AllKeys.Where(k => k.StartsWith("name")).Select(p => p.Replace("name", ""));
Use:
var namesWithoutPrefix = names.Select(n => n.Substring(4));
Doing Replace instead of Substring might replace several substrings in one name (and is slower even if it doesn't do so).
n was ten million charaters long. To do Substring(4), you just have to copy the last 9'999'996 chars over to a new string instance. To do Replace("name", ""), you would have to check all positions (nearly ten million positions) to see if the four chars 'n','a','m','e' occur in this order, and only copy over to the new string when they don't. The latter will be slower.I would not recommend relying on the position of the numeric value or the length of the string or the fact that the text reads 'name' at all. Instead you can use a simple regular expression to extract it consistently:
Regex regex = new Regex(@"[0-9]+");
var numbers = ConfigurationManager.AppSettings
.AllKeys.Select(p => regex.Match(p).Value).ToArray();
