Here's a piece of code:
data <- data.frame(a=runif(20),b=runif(20),subject=rep(1:2,10)) %>%
group_by(subject) %>%
do(distance = dist(.))
#no dplyr
intermediate <- lapply(data$distance,as.matrix)
mean.dists <- apply(simplify2array(intermediate),MARGIN = c(1,2),FUN=mean)
#dplyr
mean.dists <- lapply(data$distance,as.matrix) %>%
apply(simplify2array(.),MARGIN=c(1,2),FUN=mean)
Why does the "no dplyr" version work, and the "dplyr" version throws the error, "dim(X) must have a positive length"? They seem identical to me.
The issue is that you haven't quite fully implemented the pipe line. You are using magrittr
here, and the issue has little to do with dplyr
data$distance %>%
lapply(as.matrix ) %>%
simplify2array %>%
apply(MARGIN=1:2, FUN=mean)
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