dplyr中的长变量名称失败

Question

dplyr中超过39个字符的字符串失败，返回错误：＆＃34;错误：索引越界＆＃34;。

我错过了什么或这是一个错误吗？

40个字符不起作用：

library(dplyr)

names(iris)[5]   <- "vvv_5vvv10vvv15vvv20vvv25vvv30vvv35vvv40"

iris %>% dplyr::group_by(  vvv_5vvv10vvv15vvv20vvv25vvv30vvv35vvv40 ) %>%

  dplyr::summarise( n() )

给我错误： 错误：索引越界

39个字符有效：

names(iris)[5]   <- "vvv_5vvv10vvv15vvv20vvv25vvv30vvv35vv39"

iris %>% dplyr::group_by(  vvv_5vvv10vvv15vvv20vvv25vvv30vvv35vv39 ) %>%

  dplyr::summarise( n() )

工作正常。给了我这个（期望的）输出

Source: local data frame [3 x 2]

      vvv_5vvv10vvv15vvv20vvv25vvv30vvv35vv39 n()
    1                                  setosa  50
    2                              versicolor  50
    3                               virginica  5

SessionInfo（）

> sessionInfo()
R version 3.1.1 (2014-07-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=Danish_Denmark.1252  LC_CTYPE=Danish_Denmark.1252    LC_MONETARY=Danish_Denmark.1252 LC_NUMERIC=C                   
[5] LC_TIME=Danish_Denmark.1252    

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

other attached packages:
[1] dplyr_0.3.0.2

loaded via a namespace (and not attached):
[1] assertthat_0.1 DBI_0.3.1      lazyeval_0.1.9 magrittr_1.0.1 parallel_3.1.1 Rcpp_0.11.3    tools_3.1.1  

Answer 1

这似乎是a known issue，需要在dplyr 0.3.1中修复。来自@romainfrancois在帖子中的回复：

“它发生在这里[...]

new_groups <- lazyeval::auto_name(new_groups)

，因为：

lazyeval::auto_name
function (x, max_width = 40)
{
    names(x) <- auto_names(x, max_width = max_width)
    x
}
<environment: namespace:lazyeval>

“

<强>更新
在dplyr 0.4.0“group_by()支持超过39个字符的变量，这要归功于lazyeval”中的修复：

library(dplyr)
# Variable name with 40 characters
names(iris)[5] <- "vvv_5vvv10vvv15vvv20vvv25vvv30vvv35vvv40"

iris %>% 
  group_by(vvv_5vvv10vvv15vvv20vvv25vvv30vvv35vvv40) %>%
  summarise(n())
#   vvv_5vvv10vvv15vvv20vvv25vvv30vvv35vvv40 n()
# 1                                   setosa  50
# 2                               versicolor  50
# 3                                virginica  50