Use #average in correlations

Author: jecisc

src/DataFrame-Math/DataPearsonCorrelationMethod.class.st

@@ -11,8 +11,8 @@ DataPearsonCorrelationMethod class >> between: x and: y [
 	| xDeviation yDeviation |
 	x size = y size ifFalse: [ SizeMismatch signal: 'Correlation can not be calculated for two series of different size' ].
 
-	xDeviation := (x values replaceAll: nil with: 0) - (x sum / x size).
-	yDeviation := (y values replaceAll: nil with: 0) - (y sum / y size).
+	xDeviation := (x values replaceAll: nil with: 0) - x average.
+	yDeviation := (y values replaceAll: nil with: 0) - y average.
 
 	^ (xDeviation * yDeviation) sum / ((xDeviation ** 2) sum * (yDeviation ** 2) sum) sqrt
 ]

src/DataFrame-Tests/DataFrameStatsTest.class.st

@@ -73,7 +73,7 @@ DataFrameStatsTest >> testCorrelationMatrixWithNils [
 	df := DataFrame withRows: #( #( 1 1 ) #( 2 nil ) #( nil 3 ) #( 4 4 ) ).
 	df columnNames: #( dogs cats ).
 
-	expectedCorrelationMatrix := DataFrame withRows: #( #( 1 0.3207134902949093 ) #( 0.3207134902949093 1 ) ).
+	expectedCorrelationMatrix := DataFrame withRows: #( #( 1 0.4174555390689118 ) #( 0.4174555390689118 1 ) ).
 	expectedCorrelationMatrix columnNames: #( dogs cats ).
 	expectedCorrelationMatrix rowNames: #( dogs cats ).