How to perform set subtraction on arrays in C#?
What's the simplest way to perform a set subtraction given two arrays in C#? Apparently this is dead easy in Ruby. Basically I just want to remove the elements from array a
that are in array b
:
string[] a = new string[] { "one", "two", "three", 开发者_JAVA百科"four" };
string[] b = new string[] { "two", "four", "six" };
string[] c = a - b; // not valid
c
should equal { "one", "three" }
. b - a
would yield { "six" }
.
If you're using Linq, you can use the Except operator like this:
string [] c = a.Except(b).ToArray();
Edit: CodeInChaos makes a good point. If a
contains duplicates, it will remove any duplicates as well. The alternative to make it function exactly like the Ruby version would be this:
string [] c = a.Where(x=>!b.Contains(x)).ToArray();
public static IEnumerable<T> Minus<T>(this IEnumerable<T> enum1, IEnumerable<T> enum2)
{
Dictionary<T, int> elements = new Dictionary<T, int>();
foreach (var el in enum2)
{
int num = 0;
elements.TryGetValue(el, out num);
elements[el] = num + 1;
}
foreach (var el in enum1)
{
int num = 0;
if (elements.TryGetValue(el, out num) && num > 0)
{
elements[el] = num - 1;
}
else
{
yield return el;
}
}
}
This won't remove duplicates from enum1. To be clear:
- { 'A', 'A' } - { 'A' } == { 'A' }
- { 'A', 'A' } - { 'A' } == { }
I do the first, Enumerable.Except does the second.
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