data.table 抛出“找不到对象”错误[重复]

我有一个数据表：

library(data.table)
mydt <- data.table(index = 1:10)

当我在全局环境中尝试它时，我可以让它工作，但当我在调试器中或在包测试中使用它时却无法工作。

问题是我无法以标准方式将其子集化。

Browse[2]> mydt[,index]
Error in `[.data.frame`(x, i, j) : object 'index' not found
Browse[2]> mydt[,list(index)]
Error in `[.data.frame`(x, i, j) : object 'index' not found

这是一个可重现的示例，其中我创建了一个包，然后在评估名为的函数时收到错误myfunction:

library(devtools)
setwd(tempdir())
# make dummy package called foo
create("foo")
setwd("foo")

# add data.table as a package dependency
a <- readLines("DESCRIPTION")
depends.idx <- grepl("Depends", a)
a[depends.idx] <- paste0(a[depends.idx], ", data.table")
writeLines(a, "DESCRIPTION")

# create a dummy function 
writeLines("myfunction <- function() {a <- data.table(b=1); return(a[,b])}",
            "R/foo.R")

# check and throw error
check()
library(foo)
myfunction()

这是会话信息：

Browse[2]> sessionInfo()
R version 3.0.2 (2013-09-25)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C         LC_TIME=C            LC_COLLATE=C         LC_MONETARY=C       
 [6] LC_MESSAGES=C        LC_PAPER=C           LC_NAME=C            LC_ADDRESS=C         LC_TELEPHONE=C      
[11] LC_MEASUREMENT=C     LC_IDENTIFICATION=C 

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] PEcAn.data.atmosphere_1.3.3 data.table_1.9.2            RPostgreSQL_0.4             PEcAn.settings_1.3.3       
 [5] lubridate_1.3.3             PEcAn.DB_1.3.3              DBI_0.2-7                   PEcAn.utils_1.3.3          
 [9] udunits2_0.6                ncdf4_1.12                  randtoolbox_1.14            rngWELL_0.10-2             
[13] ggplot2_1.0.0               XML_3.98-1.1                plyr_1.8.1                  abind_1.4-0                
[17] testthat_0.8.1              devtools_1.5.0.99          

loaded via a namespace (and not attached):
 [1] MASS_7.3-29      RCurl_1.95-4.1   Rcpp_0.11.2      colorspace_1.2-4 digest_0.6.4     evaluate_0.5.5   grid_3.0.2      
 [8] gtable_0.1.2     httr_0.3         memoise_0.2.1    munsell_0.4.2    parallel_3.0.2   proto_0.3-10     reshape2_1.4    
[15] roxygen2_4.0.1   scales_0.2.4     stringr_0.6.2    tools_3.0.2      whisker_0.3-2      

很好的可重复问题！这是我得到的。您也没有发布您的输出，所以也许您在我这里没有得到相同的输出。我已经分割了输出并放置HERE问题可能出在哪里。

$ R
R version 3.1.0 (2014-04-10) -- "Spring Dance"
Copyright (C) 2014 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

> library(devtools)
> setwd(tempdir())
> # make dummy package called foo
> create("foo")
Creating package foo in .
No DESCRIPTION found. Creating with values:

Package: foo
Title: 
Description: 
Version: 0.1
Authors@R: # getOptions('devtools.desc.author')
Depends: R (>= 3.1.0)
License: # getOptions('devtools.desc.license')
LazyData: true
> setwd("foo")
> 
> # add data.table as a package dependency
> a <- readLines("DESCRIPTION")
> depends.idx <- grepl("Depends", a)
> a[depends.idx] <- paste0(a[depends.idx], ", data.table")
> writeLines(a, "DESCRIPTION")
> 
> # create a dummy function 
> writeLines("myfunction <- function() {a <- data.table(b=1); return(a[,b])}",
+             "R/foo.R")
> 
> # check and throw error
> check()
Loading required package: roxygen2
Updating foo documentation
Loading foo

HERE :

Invalid DESCRIPTION:
Authors@R field gives no person with author role.
Authors@R field gives no person with maintainer role and email address.

See the information on DESCRIPTION files in section 'Creating R packages' of the 'Writing R Extensions' manual.

Loading required package: data.table
data.table 1.9.2  For help type: help("data.table")

Attaching package: ‘data.table’

The following object is masked from ‘package:bit’:

    setattr

Updating collate directive in  /tmp/Rtmp0h3yz9/foo/DESCRIPTION 
Updating namespace directives
Writing foo.Rd
'/usr/lib/R/bin/R' --vanilla CMD build '/tmp/Rtmp0h3yz9/foo' --no-manual --no-resave-data 

* checking for file '/tmp/Rtmp0h3yz9/foo/DESCRIPTION' ... OK
* preparing 'foo':

HERE :

* checking DESCRIPTION meta-information ... ERROR
Authors@R field gives no person with author role.
Authors@R field gives no person with maintainer role and email address.

See the information on DESCRIPTION files in section 'Creating R
packages' of the 'Writing R Extensions' manual.

Error: Command failed (1)
> library(foo)
> myfunction()
Error in `[.data.frame`(x, i, j) : object 'b' not found
>