根据数据帧中其他列的分组值计算列的平均值[重复]

我无法生成值列的平均值。这是一个类似/重复的问题,我 posted earlier.

library(dplyr)

df <- data.frame(Dose   = c(1, 1, 1, 1, 1, 1, 10, 10, 10, 10, 10, 10),
                 Route  = c('IV','IV','IV','PO','PO','PO','IV','IV','IV','PO','PO','PO'),
                 Timepoint = c(0.25,0.25,0.25,0.25,0.25,0.25,0.5,0.5,0.5,0.5,0.5,0.5),
                 value =    c(207,181,201,505,180,309,123,122,137,441,335,402))

mean.df <- df %>% aggregate(value~Timepoint + Dose + Route,  FUN = mean)

Error in aggregate.data.frame(., value ~ Timepoint + Dose + Route, FUN = mean) : 
'by' must be a list

当我尝试这个时:

  mean.df <-  df %>% group_by(Timepoint, Dose, Route) %>% summarize(mean_value=mean(value))

我得到的是这个,而不是一个基于时间点、剂量和路线的平均值表。

  mean_value
  1   261.9167

我错过了什么?