lubridate masking dplyr"union"但加载时没有掩码消息

我正在学习R并想知道lubridate是否应该从dplyr发出关于屏蔽"union"的消息.

在lubridate之前加载dplyr,我得到一个错误:arrange":

library(dplyr)
Attaching package: ‘dplyr’

The following objects are masked from ‘package:stats’:

filter, lag

The following objects are masked from ‘package:base’:

intersect, setdiff, setequal, union

library(lubridate)
df1 <- data.frame(c1 = "a", c2 = 1)
df2 <- data.frame(c1 = "a", c2 = 2)
union(df1, df2) %>% arrange(c1)
Error in UseMethod("arrange_") : 
  no applicable method for 'arrange_' applied to an object of class "list"

似乎联合返回一个列表而不是一个data.frame,然后排列就会跳过它:

str(union(df1, df2))
List of 3
 $ : Factor w/ 1 level "a": 1
 $ : num 1
 $ : num 2

我最终确定了lubridate有一个"联合"功能,这显然被称为代替dplyr"联合".特别要求dplyr"union"就可以了:

str(dplyr::union(df1, df2))
'data.frame':   2 obs. of  2 variables:
 $ c1: Factor w/ 1 level "a": 1 1
 $ c2: num  1 2

dplyr::union(df1, df2) %>% arrange(c1)
  c1 c2
1  a  1
2  a  2

或者,如果首先加载lubridate,一切都很好.这是一个例子(重启RStudio之后):

library(lubridate)
library(dplyr)

Attaching package: ‘dplyr’

The following objects are masked from ‘package:lubridate’:

intersect, setdiff, union

The following objects are masked from ‘package:stats’:

filter, lag

The following objects are masked from ‘package:base’:

intersect, setdiff, setequal, union

df1 <- data.frame(c1 = "a", c2 = 1)
df2 <- data.frame(c1 = "a", c2 = 2)
union(df1, df2) %>% arrange(c1)
  c1 c2
1  a  1
2  a  2 

线索是看到dplyr掩盖了来自lubridate的"联盟"(虽然,第一条线索是"没有适用的方法"的消息,但我还不知道发生了什么 - 我下次会).但是,我原本预计,当在dplyr之后加载lubridate时,会发出类似的消息,表明lubridate将从dplyr屏蔽"union".是否有这样的消息没有出现的原因？也许我需要在我的设置中启用它？

我在Windows 7上使用RStudio版本0.99.489,R版本3.2.3,dplyr版本0.4.3和lubridate版本1.5.0.