R中的attach()问题

Question

我在R中有一个列表,我附上了.

> 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,我的名单真的很重要

> 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"   

我列表中的grData数据框有11行:

> 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,当我尝试调用grData没有myList中,我得到0行数据帧

> 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  

UPD.globalEnv中没有grData对象

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

哪里可能有问题？

Answer 1

attach()许多R风格指南(例如http://google-styleguide.googlecode.com/svn/trunk/google-r-style.html#attach)实际上并不推荐使用它,因为它可能导致错误的结果.

根据https://www.r-bloggers.com/to-attach-or-not-attach-that-is-the-question/的建议,您有三个更好的选择:

1. 直接引用变量(例如lm(ds$x ~ ds$y))
2. 指定支持此命令的命令的数据帧(例如lm(y ~ x, data=ds))
3. 使用with()函数,它返回被评估的任何表达式的值(例如with(ds,lm(y ~x)))(另请注意within()函数,它类似于with(),但返回一个修改过的对象.)

如果您仍想使用attach()所有替代品,我建议您提供完全可重复的示例.通过阅读您的代码,您似乎提供了一个不完整的输出(有一次您将列表引用为myList,其他您将其引用为RollingMau).