Question

这是一个示例df，我想从中提取大写字母：

df <- data.frame(a = c(1:5), b = c("Words are Here", "Okay", "Be Good Now", "WTF are you Doing", "it's good"))

使用str_extract_all(df$b, "[A-Z]", simplify = )时，我会得到所有大写字母的列表使用simple = TRUE：

    [,1] [,2] [,3] [,4]
[1,] "W"  "H"  ""   ""  
[2,] "O"  ""   ""   ""  
[3,] "B"  "G"  "N"  ""  
[4,] "W"  "T"  "F"  "D" 
[5,] ""   ""   ""   ""

或用simple = FALSE：

[[1]]
[1] "W" "H"

[[2]]
[1] "O"

[[3]]
[1] "B" "G" "N"

[[4]]
[1] "W" "T" "F" "D"

[[5]]
character(0)

我不知道如何采用这些方法来获得所需的输出，该输出是像这样的向量：

("WH", "O", "BGN", "WTFD", "")

Answer 1

我们可以使用gsub来匹配一个或多个不是大写字母的字符，然后将其替换为空白（""）

gsub("[^A-Z]+", "", df$b)
#[1] "WH"   "O"    "BGN"  "WTFD" ""