I'm trying to compute a mean on my data but I'm struggling with 2 things: 1. getting the right layout and 2. including the missing values in the outcome.

```
#My input data:
Stock <- c("A", "A", "A", "A", "A", "A", "B", "B", "B", "B", "B", "B")
Soil <- c("Blank", "Blank", "Control", "Control", "Clay", "Clay", "Blank", "Blank", "Control", "Control", "Clay", "Clay")
Nitrogen <- c(NA, NA, 0, 0, 20, 20, NA, NA, 0, 0, 20, 20)
Respiration <- c(112, 113, 124, 126, 139, 137, 109, 111, 122, 124, 134, 136)
d <- as.data.frame(cbind(Stock, Soil, Nitrogen, Respiration))

#The outcome I'd like to get:
Stockr <- c("A", "A", "A", "B", "B", "B")
Soilr <- c("Blank", "Control", "Clay", "Blank", "Control", "Clay")
Nitrogenr <- c(NA, 0, 20, NA, 0, 20)
Respirationr <- c(111, 125, 138, 110, 123, 135)
result <- as.data.frame(cbind(Stockr, Soilr, Nitrogenr, Respirationr))

```

Many thanks in advance for your help!