C# Extract that removes from source as many records as many in second

Question

We have two arrays

int[] arr1 = new int[] { 1, 1, 1, 2, 3 };
int[] arr2 = new int[] { 1, 2 };

I am looking for Linq (not necessary) method that accepts these two collections and returns

{ 1, 1, 3 }

The problems is that Intersect returns { 3 }

Answer 1

You can compute frequencies of the items to remove (arr2) and then remove them from arr1

var freq = arr2
  .GroupBy(item => item)
  .ToDictionary(group => group.Key, group => group.Count());

var result = arr1
  .Where(item => !freq.ContainsKey(item) || --freq[item] >= 0)
  .ToArray();