string - str_split 和 strsplit 之间的行为不一致

Question

stringr 包中 str_split 的文档指出，对于模式参数:

If "" splits into individual characters.

这表明它在这方面的行为与 strsplit 相同。然而，

library(stringr)
str_split("abcab","")
[[1]]
[1] ""  "a" "b" "c" "a" "b"

以空字符串开头。相比之下，

strsplit("abcab","")
[[1]]
[1] "a" "b" "c" "a" "b"

在非空字符串上拆分时，前导空字符串似乎是正常行为，

strsplit("abcab","ab")
[[1]]
[1] ""  "c"

但即便如此，str_split 也会生成一个“额外”尾随空字符串:

str_split("abcab","ab")
[[1]]
[1] ""  "c" "" 

这种差异是文档中的错误、功能、错误还是只是“预期行为”的不同概念？

Answer 1

如果您使用逗号作为分隔符，“预期”(您的里程可能会有所不同)结果会更加明显:

# expect "" "2" "3" "4" ""

strsplit(",2,3,4,", ",")
# [[1]]
# [1] ""  "2" "3" "4"

str_split(",2,3,4,", ",")
# [[1]]
# [1] ""  "2" "3" "4" "" 

如果我有 n 个逗号，那么我期望返回 (n+1) 元素。所以我更喜欢 str_split 的结果。但是，我不一定将其称为 strsplit 中的错误，因为它的执行效果如广告所示:

(from ?strplit) Note that this means that if there is a match at the beginning of a (non-empty) string, the first element of the output is ‘""’, but if there is a match at the end of the string, the output is the same as with the match removed.

"" 比较棘手，因为无法计算 "" 在字符串中出现的次数。因此将其视为特殊情况似乎是合理的。

(from ?str_split) If ‘""’ splits into individual characters.

基于此，我建议您发现了一个错误，应该采纳哈德利的建议并报告它!