# Problem while implementing the correlation coefficient • ### Question

• I'm new to PowerBi/powerquery and I was trying to write a function that calculates the correlation coefficient of 2 given lists.

```let
Function = (l1 as list , l2 as list) =>
let
CorCoefNumerator = List.Sum((l1 - List.Average(l1)) * (l2 -
List.Average(l2))),
Denominator1 = List.Sum(Number.Power(l1 - List.Average(l1), 2)),
Denominator2 = List.Sum(Number.Power(l2 - List.Average(l2), 2)),
CorCoefDenominator = Number.Sqrt(Denominator1 - Denominator2),
CorCoef = Value.Divide(CorCoefNumerator, CorCoefDenominator)
in
CorCoef
in
Function(Table.ToList([Sales]), Table.ToList([Profit]))```The Error message I'm getting is :
An error occurred in the ‘’ query. Expression.Error: There is an unknown identifier. Did you use the ````[field] shorthand for a _[field] outside of an 'each' expression?``One more question : Is there a way to use DAX function while writing power query queries ? becaus when ``first I tried to compute this correlation coefficient I needed it to work on columns, but since  I ``couldn't use the DAX functions I had to use my columns as Lists  !````
Monday, July 22, 2019 2:57 PM

• `(listX as list, listY as list) as number => let    SeriesCountX = List.Count(listX),    SeriesCountY = List.Count(listY),    Covariance =  List.Covariance(listX,listY)*SeriesCountX/(SeriesCountX-1),    StandardDeviationSeries1 = List.StandardDeviation(listX),    StandardDeviationSeries2 = List.StandardDeviation(listY),    CorrelationCoefficient = if SeriesCountX = SeriesCountY then                                Covariance/(StandardDeviationSeries1*StandardDeviationSeries2)                             else error "The lists must have the same number of elements"in    CorrelationCoefficient`