Question

这是一个非常小的问题，但我想了解到底发生了什么。

说我做了以下事情：

library(RMySQL)
con <- dbConnect(MySQL(), host="some.server.us-east-1.rds.amazonaws.com",user="aUser", password="password", dbname="mydb")

values1 <- dbGetQuery(con,"select x,y from table1")
attach(values1)

此时，我可以做到

rm(list=ls())

values2 <- dbGetQuery("select x,y from table1")
attach(values2)

但附件给了我关于屏蔽x和y的警告。我以为我已经破坏了那些。到底是怎么回事？如何彻底清除工作区？

Answer 1

attach()不会在您的全球环境中制作x和y的副本，它会将数据框附加到搜索路径。

来自?attach：

The database is not actually attached.  Rather, a new environment
 is created on the search path and the elements of a list
 (including columns of a data frame) or objects in a save file or
 an environment are _copied_ into the new environment.  If you use
 ‘<<-’ or ‘assign’ to assign to an attached database, you only
 alter the attached copy, not the original object.  (Normal
 assignment will place a modified version in the user's workspace:
 see the examples.)  For this reason ‘attach’ can lead to
 confusion.

例如：

> search()
[1] ".GlobalEnv"        "package:stats"     "package:graphics" 
[4] "package:grDevices" "package:utils"     "package:datasets" 
[7] "package:methods"   "Autoloads"         "package:base"     
> a <- data.frame(stuff=rnorm(100))
> search()
[1] ".GlobalEnv"        "package:stats"     "package:graphics" 
[4] "package:grDevices" "package:utils"     "package:datasets" 
[7] "package:methods"   "Autoloads"         "package:base"     
> attach(a)
> search()
 [1] ".GlobalEnv"        "a"                 "package:stats"    
 [4] "package:graphics"  "package:grDevices" "package:utils"    
 [7] "package:datasets"  "package:methods"   "Autoloads"        
[10] "package:base"     
> rm(list=ls())
> search()
 [1] ".GlobalEnv"        "a"                 "package:stats"    
 [4] "package:graphics"  "package:grDevices" "package:utils"    
 [7] "package:datasets"  "package:methods"   "Autoloads"        
[10] "package:base"     
> stuff
  [1] -0.91436377  0.67397624  0.62891651 -0.99669584  2.07692590 -0.62702302
  [...]
> detach(a)
> search()
[1] ".GlobalEnv"        "package:stats"     "package:graphics" 
[4] "package:grDevices" "package:utils"     "package:datasets" 
[7] "package:methods"   "Autoloads"         "package:base"

Answer 2

提一下......如果您或许在您的环境中隐藏了对象，例如.First和.Last函数，则可以使用rm(list = ls(all.names = TRUE))删除它们。但在您的情况下，使用detach(objectname)从搜索路径中删除对象。 detach()将移除位置＃2中的任何对象，因为无法删除.GlobalEnv（以及base）。使用detach()，您可以卸载以前加载的软件包，因此请小心（尽管您始终可以使用library(packagename)加载它们。）

Answer 3

R本身在rm的帮助中说：

## remove (almost) everything in the working environment.
## You will get no warning, so don't do this unless you are really sure.
rm(list = ls())

注意'差不多'。有不同的环境。

你试过detach(values1)吗？

Answer 4

您很可能至少有一个其他数据框或列表附有x和y列/组件。您可以使用“冲突”功能查看具有潜在冲突的所有对象，并使用“查找”功能找出这些对象的位置（“搜索”功能也有助于显示您附加的所有内容）。

您的问题是为什么附加数据框架不受欢迎的一个很好的例子，最好使用“with”或“within”之类的函数，以免忘记分离对象时出现问题。

Answer 5

要使用detach（）函数从Work Space中删除特定包，它需要包的完整描述。

示例：删除包ISwR 答案1：分离（ISwR）......不行！套餐仍在工作区。答案2：分离（包裹：ISWR）....工作！包将从工作空间中删除。

Answer 6

如果您正在使用RStudio，您可以转到Session-＆gt; Clear Workspace ... 清除工作区中的所有变量

Answer 7

您可以使用：

rm(list=ls())

或：

rm(list=(ls()))

但在关闭R之前保存工作区。

rm（list = ls（））不能完全清除工作区

7 个答案: