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Problems with attach() in R

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

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 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

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

UPD. There is no grData object in globalEnv

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

Where could be problem?

Solution

  • 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.

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

    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.)

    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).