LINQ does not start with on List<string>

I have a List<string> with five strings in it:

abc
def
ghi
jkl
mno

I have another string, "pq", and I nee开发者_如何学编程d to know if each string in the list does not start with "pq" - how would I do that with LINQ (.NET 4.0)?

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Two options: Any and All. Which one you should use depends on what you find more readable:

var allNonPq = myList.All(x => !x.StartsWith("pq"));
var notAnyPq = !myList.Any(x => x.StartsWith("pq"));

These are effectively equivalent in efficiency - both will stop as soon as they reach an element starting with "pq" if there is one.

If you find yourself doing this a lot, you could even write your own extension method:

public static bool None<T>(this IEnumerable<T> source, Func<T, bool> predicate)
{
    return !source.Any(predicate);
}

at which point you'd have:

var nonePq = myList.None(x => x.StartsWith("pq"));

Whether you find that more readable than the first two is a personal preference, of course :)

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bool noPQStart = !myList.Any( x=> x.StartsWith("pq"));

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This will produce results which is an IEnumerable<bool>

var strings = new string[] { ... };
var results = strings.Select(s => s.StartsWith("pq"));

---

var notPq = from s in myList where  !s.StartsWith("pq") select s;

if (notPq.Any()) {
  // At least one item in list doesn't start with pq, possibly do something with each element that doesn't
}