不能对R中的data.table使用dput [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")"

问题在哪里，如何纠正？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 外部指针地址（这是 data.table 在内部使用，并将在需要时重建），这是你不能真正使用的。

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.

如果你手动切出 .internal.selfref 部分，它会工作正常，除了<$ c $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.

您可以向 data.table 添加一个FR $ c>关于这一点，但它将需要修改 data.table 中的基函数，类似于 rbind 目前处理。

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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