How to subset data for a specific column with ddply?

Question

I would like to know if there is a simple way to achieve what I describe below using ddply. My data frame describes an experiment with two conditions. Participants

Answer 1

Using dplyr package:

library(dplyr)
df %>%
  group_by(Condition) %>%
  summarise(N = n(),
            nAccurate = sum(Accuracy),
            RT = mean(RT[Accuracy == 1]))

Answer 2

With plyr, you can do it as follows:

ddply(df,
      .(Condition), summarise, 
      N          = length(Response),
      nAccurate  = sum(Accuracy),
      RT         = mean(RT[Accuracy==1]))

this gives:

   Condition N nAccurate     RT
1:         1 6         4 127.50
2:         2 6         4 300.25

If you use data.table, then this is an alternative way:

library(data.table)
setDT(df)[, .(N = .N,
              nAccurate = sum(Accuracy),
              RT = mean(RT[Accuracy==1])),
          by = Condition]