R strsplit不会拆分为"."？

我正在编写一个R脚本,并希望定义一个变量,以便在绘图注释中用作文件名的一部分.我以为我会使用strsplit()函数.这是我的代码和输出:

infile = "ACC_1346.table.txt"

x = strsplit(infile, ".")

class(infile)
[1] "character"

class(x)
[1] "list"

str(x)
List of 1
$ : chr [1:18] "" "" "" "" ...

x[[1]]
[1] "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" "" ""

我预计最终的输出是:

[1] "ACC_1346" "table" "txt"

这里发生了什么？

为了避免正则表达式fixed = TRUE在调用中完全使用strsplit

infile = "ACC_1346.table.txt"
x = strsplit(infile, ".", fixed = TRUE)

x

[[1]]
[1] "ACC_1346" "table" "txt"