不能将 dput 用于 R 中的 data.table [英] Cannot use dput for data.table in R

问题描述

我有以下 data.table 我不能使用 dput 命令的输出来重新创建它:

I have following data.table for which I cannot use output of dput command to recreate it:

> ddt
   Unit Anything index new
1:    A      3.4     1   1
2:    A      6.9     2   1
3:   A1      1.1     1   2
4:   A1      2.2     2   2
5:    B      2.0     1   3
6:    B      3.0     2   3
> 
> 
> str(ddt)
Classes ‘data.table’ and 'data.frame':  6 obs. of  4 variables:
 $ Unit    : Factor w/ 3 levels "A","A1","B": 1 1 2 2 3 3
 $ Anything: num  3.4 6.9 1.1 2.2 2 3
 $ index   : num  1 2 1 2 1 2
 $ new     : int  1 1 2 2 3 3
 - attr(*, ".internal.selfref")=<externalptr> 
 - attr(*, "sorted")= chr  "Unit" "Anything"
> 
> 
> dput(ddt)
structure(list(Unit = structure(c(1L, 1L, 2L, 2L, 3L, 3L), .Label = c("A", 
"A1", "B"), class = "factor"), Anything = c(3.4, 6.9, 1.1, 2.2, 
2, 3), index = c(1, 2, 1, 2, 1, 2), new = c(1L, 1L, 2L, 2L, 3L, 
3L)), .Names = c("Unit", "Anything", "index", "new"), row.names = c(NA, 
-6L), class = c("data.table", "data.frame"), .internal.selfref = <pointer: 0x8948f68>, sorted = c("Unit", 
"Anything"))
> 

粘贴时出现以下错误:

> dt = structure(list(Unit = structure(c(1L, 1L, 2L, 2L, 3L, 3L), .Label = c("A", 
+ "A1", "B"), class = "factor"), Anything = c(3.4, 6.9, 1.1, 2.2, 
+ 2, 3), index = c(1, 2, 1, 2, 1, 2), new = c(1L, 1L, 2L, 2L, 3L, 
+ 3L)), .Names = c("Unit", "Anything", "index", "new"), row.names = c(NA, 
+ -6L), class = c("data.table", "data.frame"), .internal.selfref = <pointer: 0x8948f68>, sorted = c("Unit", 
Error: unexpected '<' in:
"3L)), .Names = c("Unit", "Anything", "index", "new"), row.names = c(NA, 
-6L), class = c("data.table", "data.frame"), .internal.selfref = <"
> "Anything"))
Error: unexpected ')' in ""Anything")"

问题出在哪里，如何解决?感谢您的帮助.

Where is the problem and how can it be corrected? Thanks for your help.

推荐答案

问题是 dput 打印出外部指针地址(这是 data.table 使用的东西内部，并在需要时重建)，你不能真正使用.

The problem is that dput prints out external pointer address (this is something that data.table uses internally, and will reconstruct when required), which you can't really use.

如果您手动删除 .internal.selfref 部分，它会正常工作，除了 data.table 对某些操作的一次性投诉.

If you manually cut out the .internal.selfref part, it will work just fine, except for a one-time complaint from data.table for some operations.

你可以在 data.table 中添加一个关于这个的 FR，但这需要修改 data.table 的基本函数，类似于 rbind 目前正在处理中.

You could add an FR to data.table about this, but it will require modifying the base function from data.table, similar to how rbind is currently handled.

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