Add Exclude Values From An Array as a Ruby til

ruby/exclude-values-from-an-array.md

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+# Exclude Values From An Array
+
+In true Ruby fashion, there are all sorts of ways to exclude values from an
+array.
+
+If you just want to exclude `nil` values, you can use
+[`#compact`](https://ruby-doc.org/core-3.0.0/Array.html#method-i-compact).
+
+```ruby
+> [1,nil,:what,4].compact
+#=> [1, :what, 4]
+```
+
+If you want to exclude `nil` values and some other named value, you could use
+[`#filter`](https://ruby-doc.org/core-3.0.0/Array.html#method-i-filter) or
+[`#reject`](https://ruby-doc.org/core-3.0.0/Array.html#method-i-reject).
+
+```ruby
+> [1,nil,:what,4].filter { |val| !val.nil? && val != :what }
+#=> [1, 4]
+> [1,nil,:what,4].reject { |val| val.nil? || val == :what }
+#=> [1, 4]
+```
+
+The filter is clumsy and heavy-handed for this sort of example. A really terse
+way of doing the same thing is with set difference:
+[`#-`](https://ruby-doc.org/core-3.0.0/Array.html#method-i-2D).
+
+```ruby
+> [1,nil,:what,nil,5] - [:what,nil]
+#=> [1, 5]
+```
+
+Or the spelled out
+[`#difference`](https://ruby-doc.org/core-3.0.0/Array.html#method-i-difference)
+method.
+
+```ruby
+> [1,nil,:what,nil,5].difference([:what,nil])
+#=> [1, 5]
+```