尝试在R中首次尝试OO编程时，我声明了一个S4对象TestObject，它有两个插槽，其中一个插槽（test.df）具有data.frame允许的类：
library("dplyr")
library("methods")
# Declare S4 Object
setClass("TestObject",
slots = list(test.mat = "matrix",
test.df = "data.frame"))
令我惊讶的是，当我尝试分配tbl_df“class”的对象时：
library("nycflights13")
class(flights)
## [1] "tbl_df" "tbl" "data.frame"
它会抛出错误：
test.object <- new("TestObject")
slot(test.object, "test.mat") <- matrix(rnorm(10), 5, 2)
slot(test.object, "test.df") <- flights
## Error in checkSlotAssignment(object, name, value): c("assignment of an object of class \"tbl_df\" is not valid for slot 'test.df' in an object of class \"TestObject\"; is(value, \"data.frame\") is not TRUE", "assignment of an object of class \"tbl\" is not valid for slot 'test.df' in an object of class \"TestObject\"; is(value, \"data.frame\") is not TRUE", "assignment of an object of class \"data.frame\" is not valid for slot 'test.df' in an object of class \"TestObject\"; is(value, \"data.frame\") is not TRUE")
我的印象是tbl_df只是包装了一个data.frame。我想也许我可以将tbl_df声明为test.df的允许类：
setClass("TestObject",
slots = list(test.mat = "matrix",
test.df = "tbl_df"))
## Warning: undefined slot classes in definition of "TestObject":
## test.df(class "tbl_df")
但似乎并没有将其视为允许的类别。
似乎我必须将tbl_df转换为data.frame，才能完成这项工作......
setClass("TestObject",
slots = list(test.mat = "matrix",
test.df = "data.frame"))
slot(test.object, "test.df") <- as.data.frame(flights)
## [1] "data.frame"
但这样做会失去将它作为tbl_df的好处（例如打印几行，所有列都适合一个屏幕等）
class(slot(test.object, "test.df"))
head(slot(test.object, "test.df"))
## year month day dep_time dep_delay arr_time arr_delay carrier tailnum
## 1 2013 1 1 517 2 830 11 UA N14228
## 2 2013 1 1 533 4 850 20 UA N24211
## 3 2013 1 1 542 2 923 33 AA N619AA
## 4 2013 1 1 544 -1 1004 -18 B6 N804JB
## 5 2013 1 1 554 -6 812 -25 DL N668DN
## 6 2013 1 1 554 -4 740 12 UA N39463
## flight origin dest air_time distance hour minute
## 1 1545 EWR IAH 227 1400 5 17
## 2 1714 LGA IAH 227 1416 5 33
## 3 1141 JFK MIA 160 1089 5 42
## 4 725 JFK BQN 183 1576 5 44
## 5 461 LGA ATL 116 762 5 54
## 6 1696 EWR ORD 150 719 5 54
我有一种感觉我不理解tbl_df（也许它不是一个类）。但是，有没有办法让tbl_df“类”与S4和data.frame允许的类一起使用？
完整的代码可以在这里找到：
https://github.com/tinyheero/tbl-df-s4/blob/master/tbl-df-s4.Rmd
相应的html：
https://htmlpreview.github.io/?https://github.com/tinyheero/tbl-df-s4/blob/master/tbl-df-s4.html
R会话详情
devtools::session_info()
## Session info --------------------------------------------------------------
## setting value
## version R version 3.2.2 (2015-08-14)
## system x86_64, darwin14.5.0
## ui X11
## language (EN)
## collate en_CA.UTF-8
## tz America/Vancouver
## date 2016-02-25
## Packages ------------------------------------------------------------------
## package * version date source
## assertthat 0.1 2013-12-06 CRAN (R 3.2.2)
## DBI 0.3.1 2014-09-24 CRAN (R 3.2.2)
## devtools 1.10.0 2016-01-23 CRAN (R 3.2.2)
## digest 0.6.9 2016-01-08 CRAN (R 3.2.2)
## dplyr * 0.4.3 2015-09-01 CRAN (R 3.2.2)
## evaluate 0.8 2015-09-18 CRAN (R 3.2.2)
## formatR 1.2.1 2015-09-18 CRAN (R 3.2.2)
## htmltools 0.3 2015-12-29 CRAN (R 3.2.2)
## knitr * 1.12.3 2016-01-22 CRAN (R 3.2.2)
## magrittr 1.5 2014-11-22 CRAN (R 3.2.2)
## memoise 0.2.1 2014-04-22 CRAN (R 3.2.2)
## nycflights13 * 0.1 2014-07-22 CRAN (R 3.2.2)
## R6 2.1.2 2016-01-26 CRAN (R 3.2.2)
## Rcpp 0.12.3 2016-01-10 CRAN (R 3.2.2)
## rmarkdown 0.9.5 2016-02-12 Github (rstudio/rmarkdown@b24f7e7)
## stringi 1.0-1 2015-10-22 CRAN (R 3.2.2)
## stringr 1.0.0 2015-04-30 CRAN (R 3.2.2)
## yaml 2.1.13 2014-06-12 CRAN (R 3.2.2)
非常感谢提前。
答案 0 :(得分：3)
从S4s的角度来看，tbl_df确实是data.frame并不清楚。您可以使用setOldClass声明该关系，您必须提供tbl_df对象的完整类名列表。这样做向S4解释'tbl_df'真的继承自data.frame：
setOldClass(c("tbl_df", "tbl", "data.frame"))
答案 1 :(得分：1)
你可以尝试：
# allow S4 to see the class tbl_df
setOldClass("tbl_df")
# Declare S4 Object
setClass(
"TestObject",
representation(
test.mat = "matrix",
test.df = "tbl_df"
)
)