Find unique combinations based on two columns and calculate the mean

问题

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

I have the following dataframe:

Image 1

I would like to:

Find the unique combinations of the columns 'Species' and 'Effects'
Report the concentration belonging to this unique combination
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

回答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))

回答2:

Create some example data:

dat <- data.frame(Species = rep.int(LETTERS[1:4], c(4, 1, 3, 2)),
                  Effect = c(rep("Reproduction", 3), "Growth", "Growth",
                             "Reproduction", "Mortality", "Mortality",
                             "Growth", "Growth"),
                  Concentration = rnorm(10))

You can use the function aggregate:

aggregate(Concentration ~ Species + Effect, dat, mean)

回答3:

Just for fun before I call it a night.... Assuming your data.frame is called "dat", here are two more options:

A data.table solution.

library(data.table)
datDT <- data.table(dat, key="Species,Effect")
datDT[, list(Concentration = mean(Concentration)), by = key(datDT)]
#    Species       Effect Concentration
# 1:       A       Growth          1.50
# 2:       A Reproduction          1.30
# 3:       B       Growth          1.60
# 4:       C    Mortality          1.05
# 5:       C Reproduction          1.20
# 6:       D       Growth          1.35

An sqldf solution.

library(sqldf)
sqldf("select Species, Effect,
      avg(Concentration) `Concentration`
      from dat
      group by Species, Effect")
#   Species       Effect Concentration
# 1       A       Growth          1.50
# 2       A Reproduction          1.30
# 3       B       Growth          1.60
# 4       C    Mortality          1.05
# 5       C Reproduction          1.20
# 6       D       Growth          1.35

来源：https://stackoverflow.com/questions/13017511/find-unique-combinations-based-on-two-columns-and-calculate-the-mean

标签

unique

dataframe