add Charter#remove to remove an event

lib/sscharter.rb

@@ -82,7 +82,7 @@ def initialize type, beat, duration_beats = nil, bpm_changes, **properties
 			@bpm_changes = bpm_changes
 			@properties = properties
 			@offset = 0.0
-			process_backtrace
+			@backtrace = caller.filter { _1.sub! /^#{PROJECT_DIR}\//, '' }
 		end
 
 		def time_at_relative_beat delta_beat
@@ -126,10 +126,6 @@ def inspect
 			"#<#@type at #@beat#{@duration_beats && " for #@duration_beats"} offset #@offset: " +
 			@properties.map { |k, v| "#{k}=#{v.inspect}" }.join(', ') + '>'
 		end
-
-		def process_backtrace
-			@backtrace = caller.filter { _1.sub! /^#{PROJECT_DIR}\//, '' }
-		end
 	end
 
 	# Implements homography
@@ -500,6 +496,10 @@ def tip_point mode, *args, **opts, &block
 		result
 	end
 
+	def remove *events
+		events.each { @events.delete _1 }
+	end
+
 	def event type, duration_beats = nil, **properties
 		raise OffsetError.new __method__ unless @bpm_changes
 		event = Event.new type, @current_beat, duration_beats, @bpm_changes, **properties

test/test_sscharter.rb

@@ -494,4 +494,27 @@ def test_bg_note
 		assert_equal event4.duration_beats, 0
 	end
 
+	def test_remove
+		chart = Charter.open __method__
+		chart.offset offset = rand
+		chart.bpm bpm = rand * 300
+
+		group1 = chart.group do
+			t rand(100), rand(100)
+			b 1
+			f rand(100), rand(100), rand*PI*2
+			b 2
+		end
+		group2 = chart.group do
+			t rand(100), rand(100)
+			b 1
+			f rand(100), rand(100), rand*PI*2
+			b 2
+		end
+		assert_equal chart.events.length, 4
+		chart.remove *group1
+		assert_equal chart.events.length, 2
+		assert_equal chart.events, group2
+	end
+
 end