R 中的 attach() 问题

问题描述

我在 R 中有一个列表，我附上了.

i have a list in R, which i attached.

> attach(myList)
> summary(myList)
            Length Class      Mode     
grData      3      data.frame list     
maxDate     1      POSIXct    numeric  
query       1      -none-     character
newData     3      data.frame list     
updateQuery 1      -none-     function

好的，我的清单真的附上了

Okay, my list is really attached

> search()
 [1] ".GlobalEnv"          "myList"          "package:xlsx"        "package:xlsxjars"   
 [5] "package:rJava"       "package:quantmod"    "package:TTR"         "package:xts"        
 [9] "package:zoo"         "package:tidyr"       "package:stringr"     "package:RPostgreSQL"
[13] "package:DBI"         "package:dplyr"       "tools:rstudio"       "package:stats"      
[17] "package:graphics"    "package:grDevices"   "package:utils"       "package:datasets"   
[21] "package:methods"     "Autoloads"           "package:base"   

grData 我列表中的数据框有 11 行:

grData data frame from my list has 11 rows:

> summary(myList$grData)
      date            application_id      value        
 Min.   :2016-10-01   Min.   : 7.0   Min.   :  5769  
 1st Qu.:2016-10-01   1st Qu.: 9.5   1st Qu.: 33113  
 Median :2016-10-01   Median :12.0   Median : 65821  
 Mean   :2016-10-01   Mean   :22.0   Mean   :106336  
 3rd Qu.:2016-10-01   3rd Qu.:37.5   3rd Qu.:108861  
 Max.   :2016-10-01   Max.   :49.0   Max.   :507376

但是当我尝试在没有 myList 的情况下调用 grData 时，我得到了 0 行的数据框

But when i try to call grData without myList, i get data frame with 0 rows

> summary(grData)
      date    application_id      value     
 Min.   :NA   Min.   : NA    Min.   : NA  
 1st Qu.:NA   1st Qu.: NA    1st Qu.: NA  
 Median :NA   Median : NA    Median : NA  
 Mean   :NA   Mean   :NaN    Mean   :NaN  
 3rd Qu.:NA   3rd Qu.: NA    3rd Qu.: NA  
 Max.   :NA   Max.   : NA    Max.   : NA  

更新.globalEnv 中没有 grData 对象

UPD. There is no grData object in globalEnv

> ls()
[1] "checkDbLag"  "con"         "i"           "newDate"     "myList"  "updateQuery"
[7] "x" 

哪里有问题?

推荐答案

attach() 的使用实际上是很多 R 风格指南(如 http://google-styleguide.googlecode.com/svn/trunk/google-r-style.html#attach)，因为它会导致错误的结果.

The use of attach() is actually not recommended by many R style guides (like http://google-styleguide.googlecode.com/svn/trunk/google-r-style.html#attach) because it can lead to wrong results.

正如 https 所建议的://www.r-bloggers.com/to-attach-or-not-attach-that-is-the-question/ 你有三个更好的选择:

As suggested by https://www.r-bloggers.com/to-attach-or-not-attach-that-is-the-question/ you have three better options:

1. 直接引用变量(例如lm(ds$x ~ ds$y))
2. 为支持此功能的命令指定数据帧(例如 lm(y ~ x, data=ds))
3. 使用 with() 函数，它返回任何表达式的计算值(例如 with(ds,lm(y ~x)))(还要注意 within() 函数，它与 with() 类似，但返回一个修改过的对象.)

1. Reference variables directly (e.g. lm(ds$x ~ ds$y))
2. Specify the dataframe for commands which support this (e.g. lm(y ~ x, data=ds))
3. Use the with() function, which returns the value of whatever expression is evaluated (e.g. with(ds,lm(y ~x)))(Also note the within() function, which is similar to with(), but returns a modified object.)

如果你仍然想使用 attach() 即使给出了所有的替代方案，我建议你提供一个完全可重现的例子.通过阅读您的代码，您似乎提供了一个不完整的输出(一次您将列表引用为 myList，另一次将其引用为 RollingMau).

If you still want to use attach() even given all the alternatives, I suggest you provide a fully reproducible example. By reading your code it seems that you are providing an incomplete output (one time you reference your list as myList, other you reference it as RollingMau).

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