I have a data frame with three different columns: Wavelength, Sample, and Mean.

Wavelength <- c(400, 400, 400, 400, 400, 400)
Sample <- c("A.1", "A.2", "A.3", "AB.1", "AB.2", "AB.3")
Mean <- c(0.434, 0.347, 0.434, 0.674, 0.591, 0.857)
df <- data.frame(Wavelength, Sample, Mean)
df
  Wavelength Sample   Mean
1        400    A.1  0.434
2        400    A.2  0.347
3        400    A.3  0.434
4        400   AB.1  0.674
5        400   AB.2  0.591
6        400   AB.3  0.857

Is there a way to group by everything before the “.” in the sample column, and then put those rows into a separate data frame? An example of what I am looking for is like this:

>df
  Wavelength Sample   Mean
1        400    A.1  0.434
2        400    A.2  0.347
3        400    A.3  0.434
>df1
  Wavelength Sample   Mean
4        400   AB.1  0.674
5        400   AB.2  0.591
6        400   AB.3  0.857

I have more than 2 groups of samples, but these are just an example of what I am trying to do.