Question

I have a problem in R, which I can’t seem to solve.

I have the following dataframe:

Image 1

I would like to:

1. Find the unique combinations of the columns ‘Species’ and ‘Effects’
2. Report the concentration belonging to this unique combination
3. If this unique combination is present more than one time, calculate the mean concentration

And would like to get the following dataframe:

Image 2

I have tried next script to get the unique combinations:

UniqueCombinations <- Data[!duplicated(Data[,1:2]),]

but don’t know how to proceed from there.

Thanks in advance for your answers!

Tina

Answer 1

Try the following (Thanks Brandon Bertelsen for nice comment):

Creating your data:

foo = data.frame(Species=c(rep("A",4),"B",rep("C",3),"D","D"), 
                 Effect=c(rep("Reproduction",3), rep("Growth",2),
                          "Reproduction", rep("Mortality",2), rep("Growth",2)), 
                 Concentration=c(1.2,1.4,1.3,1.5,1.6,1.2,1.1,1,1.3,1.4))

Using great package plyr for a bit of magic 🙂

library(plyr)
ddply(foo, .(Species,Effect), function(x) mean(x[,"Concentration"]))

And this is a bit more complicated, but cleaner version (Thanks again to Brandon Bertelsen):

ddply(foo, .(Species,Effect), summarize, mean=mean(Concentration))