我有一个包含数据框的类，其中列是因子（来自 phyloseq 包）。它看起来像这样：
> str(a)
'data.frame': 124 obs. of 21 variables:
Formal class 'sample_data' [package "phyloseq"] with 4 slots
..@ .Data :List of 21
.. ..$ : Factor w/ 2 levels "L25","L53": 2 2 2 2 2 2 2 2 1 1 ...
.. ..$ : Factor w/ 1 level "feces metagenome": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 1 level "none": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 1 level "not applicable": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 1 level "not applicable": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 1 level "feces": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 2 levels "Germany:Berlin",..: 2 2 2 2 2 2 2 2 1 1 ...
.. ..$ : Factor w/ 1 level "Mus musculus": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 1 level "not applicable": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 1 level "none": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 1 level "none": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 1 level "none": 1 1 1 1 1 1 1 1 1 1 ...
.. ..$ : Factor w/ 3 levels "female","male",..: 1 1 1 1 2 2 1 1 3 3 ...
..@ names : chr "Library" "Organism" "Collection_date" "Env_biome" ...
..@ row.names: chr "285L53" "286L53" "287L53" "288L53" ...
..@ .S3Class : chr "data.frame"
我可以毫无问题地在控制台中查看数据，但想在数据查看器中检查它。但是，如果我尝试这样做，我只会得到一个显示列名、列类型（即“因子”）以及所述因子的级别的表，如下所示
Name Type Value
a List[124x21(phyloseq::sample_data) A data.frame with 124 rows and 21 columns
Library factor Factor with 2 levels "L25", "L53"
Organism factor Factor with 1 level: "feces Metagenome"
etc.
我对 R 有点陌生，并尝试了以下方法：
View(a@.Data)
View(a)
View(a@.Data[])
我怀疑我在 S4 类及其语法方面缺乏一些知识，你能告诉我如何在数据查看器中显示实际数据吗？