将字符向量拆分为单个字符？ （与 paste 或 stringr::str_c 相对）

Question

R 中一个令人难以置信的基本问题，但解决方案尚不清楚。

如何将字符向量拆分为单个字符，即paste(..., sep='') 或stringr::str_c() 的反面？

比这更不笨重的东西：

sapply(1:26, function(i) { substr("ABCDEFGHIJKLMNOPQRSTUVWXYZ",i,i) } )
"A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S" "T" "U" "V" "W" "X" "Y" "Z"

能否以其他方式完成，例如strsplit()、stringr::* 或其他什么？

Answer 1

是的，strsplit 会这样做。 strsplit 返回一个列表，因此您可以使用 unlist 将字符串强制转换为单个字符向量，或者使用列表索引 [[1]] 访问第一个元素。

x <- paste(LETTERS, collapse = "")

unlist(strsplit(x, split = ""))
# [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S"
#[20] "T" "U" "V" "W" "X" "Y" "Z"

OR（注意实际上没有必要命名 split 参数）

strsplit(x, "")[[1]]
# [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S"
#[20] "T" "U" "V" "W" "X" "Y" "Z"

您也可以拆分NULL 或character(0) 以获得相同的结果。

Answer 2

来自stringr 的str_extract_all() 提供了一种执行此操作的好方法：

str_extract_all("ABCDEFGHIJKLMNOPQRSTUVWXYZ", boundary("character"))

[[1]]
 [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S" "T" "U"
[22] "V" "W" "X" "Y" "Z"

Answer 3

为了清晰起见，这是逐步呈现的；实际上，会创建一个函数。

查找任何字符按顺序重复的次数

the_string <- "BaaaaaaH"
# split string into characters
the_runs <- strsplit(the_string, "")[[1]]
# find runs
result <- rle(the_runs)
# find values that are repeated
result$values[which(result$lengths > 1)]
#> [1] "a"
# retest with more runs
the_string <- "BaabbccH"
# split string into characters
the_runs <- strsplit(the_string, "")[[1]]
# find runs
result <- rle(the_runs)
# find values that are repeated
result$values[which(result$lengths > 1)]
#> [1] "a" "b" "c"