Yu Deng questions

• What is mean by 'cross-validation with non-unique 'x' values seems doubtful' in Smoothing spline in R?
• How to get confidence interval for smooth.spline?
• R - Filter Data from a data frame
• R filter() dealing with NAs
• Force certain parameters to have positive coefficients in lm()
• Oracle VirtualBox "VT-x is disabled in the BIOS"
• R - Warning message: "In cor(...): the standard deviation is zero"

Yu Deng answers