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					@ -219,7 +219,7 @@ def update_std_dev(cur_mean, cur_std_dev, new_data_point, sample_size): | 
				
			
			
		
	
		
			
				
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					    Returns: | 
				
			
			
		
	
		
			
				
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					        (new_mean, new_std_dev) | 
				
			
			
		
	
		
			
				
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					    """ | 
				
			
			
		
	
		
			
				
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					    # This is an implementationof Welford's method | 
				
			
			
		
	
		
			
				
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					    # This is an implementation of Welford's method | 
				
			
			
		
	
		
			
				
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					    # http://jonisalonen.com/2013/deriving-welfords-method-for-computing-variance/ | 
				
			
			
		
	
		
			
				
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					    new_mean = ((sample_size - 1) * cur_mean + new_data_point) / sample_size | 
				
			
			
		
	
		
			
				
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					    delta_variance = (new_data_point - new_mean) * (new_data_point - cur_mean) | 
				
			
			
		
	
	
		
			
				
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