diff --git a/array_utils.rb b/array_utils.rb
new file mode 100644
index 0000000..8c58432
--- /dev/null
+++ b/array_utils.rb
@@ -0,0 +1,12 @@
+class ArrayUtils
+  class << self
+    def firsts_in_sequence(elements)
+      first = nil
+      elements.select do |cur|
+        ret = (cur != first)
+        first = cur
+        ret
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/test/array_utils_test.rb b/test/array_utils_test.rb
new file mode 100644
index 0000000..df88015
--- /dev/null
+++ b/test/array_utils_test.rb
@@ -0,0 +1,8 @@
+require 'test_helper'
+require '../array_utils'
+
+class ArrayUtilsTest < Test::Unit::TestCase
+  def test_firsts_in_sequence
+    assert_equal [1,2,1,2,3], ArrayUtils.firsts_in_sequence([1,1,1,1,2,1,1,1,2,2,2,2,2,2,2,3,3])
+  end
+end
\ No newline at end of file