regression_1 <- lm(weight  ~ morning.dummy + dayNumber + (morning.dummy*dayNumber) +
                     I(dayNumber^2) + (I(dayNumber^2)*morning.dummy),
                   data=weight_data)
summary(regression_1)
#plot
plot2 <- ggplot(data=weight_data,aes(x=dayNumber, y=weight, color=morning.dummy)) +
          geom_point()+
          stat_smooth(method = "lm", formula = weight  ~ morning.dummy + dayNumber + (morning.dummy*dayNumber) +I(dayNumber^2) + (I(dayNumber^2)*morning.dummy), size = 1) +
          labs(y = "Weight in kg", x = "Day Number of weight measurment", subtitle = "Day 0 = 3 October 2010")
plot2

Error in grid.Call.graphics(C_setviewport, vp, TRUE) :
  non-finite location and/or size for viewport
In addition: Warning message:
Computation failed in `stat_smooth()`:
object 'dayNumber' not found