与lapply和dplyr / magrittr有奇怪的错误 [英] Weird error with lapply and dplyr/magrittr

问题描述

这是一段代码：

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)

为什么no dplyr ，dplyr版本抛出错误，dim（X）必须有一个正长度？他们似乎与我相同。

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.

推荐答案

问题是您还没有完全实现管道。您正在使用 magrittr ，而且这个问题与 dplyr

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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