Optional argument for variation()

Added `corrected=true/false` for variation
Added test for the above addition

Author: itsdebartha

src/scalarstats.jl

@@ -411,7 +411,7 @@ a precomputed mean `m`. The coefficient of variation is the ratio of the
 standard deviation to the mean.
 """
 variation(x, m) = stdm(x, m) / m
-variation(x) = ((m, s) = mean_and_std(x); s/m)
+variation(x; corrected::Bool=true) = ((m, s) = mean_and_std(x; corrected=corrected); s/m)
 
 # Standard error of the mean: std / sqrt(len)
 # Code taken from var in the Statistics stdlib module

test/scalarstats.jl

@@ -164,6 +164,8 @@ z2 = [8. 2. 3. 1.; 24. 10. -1. -1.; 20. 12. 1. -2.]
 
 @test variation([1:5;]) ≈ 0.527046276694730
 @test variation(skipmissing([missing; 1:5; missing])) ≈ 0.527046276694730
+@test isnan(variation(a))
+@test variation(1; corrected = false) == 0
 
 @test @inferred(sem([1:5;])) ≈ 0.707106781186548
 @test @inferred(sem(skipmissing([missing; 1:5; missing]))) ≈ 0.707106781186548