从 R 中不同位置的字符串中提取字母

Question

我有两列，我想从不同的位置提取字母。目标是显示 Col2 中使用了什么字母来替换 Col1 中的字母。字母将根据 Position 列从 Col1 和 Col2 中提取。在位置列中，字母 "E" 表示将用于提取字母的位置。

这是我尝试使用 substr 函数的结果：

df <- data.frame ("Col1" = c("Stores","University","Street","Street Store"), 
       "Col2" = c("Ostues", "Unasersity", "Straeq","Straeq Stuwq"), 
       "Position" = c("EMMEMM","MMEEMMMMMM", "MMMEME","MMMEMEMMMEEE"), 
       "Desired Output" = c("S|O , r|u","i|a , v|s","e|a , t|q", "e|a , t|q , o|u , r|w , e|q"))


n <- which(strsplit(df$Position,"")[[1]]=="E")
#output for the first row:
# [1] 1  4

#then I used substr function:
substr(df$Col1, n, n)

#only the first character returned as below:
[1] "S"

#desired output for first row:
S|O , r|u

Answer 1

首先我会做一个辅助函数来从一个位置提取一个字符

subchr <- function(x, pos) {
  substring(x, pos, pos)
}

然后就可以找到所有要提取的位置了

extract_at <- lapply(strsplit(as.character(df$Position), ""), 
    function(x) which(x=="E"))

并将它们放在一起以获得您想要的输出

mapply(function(e, a, b){
  paste(subchr(a, e), subchr(b,e), sep="|", collapse=" , ")
}, extract_at, as.character(df$Col1), as.character(df$Col2))
# [1] "S|O , r|u" "i|a , v|s" "e|a , t|q"

Answer 2

可能是这样的：

df %>% mutate(x=str_replace_all(chartr("M",".",Position),"E","\(\.\)"),
          output=paste0(str_replace(Col1,x,"\1"),"|",str_replace(Col2,x,"\1"),
                  " , ",str_replace(Col1,x,"\2"),"|",str_replace(Col2,x,"\2")))
#        Col1       Col2   Position Desired.Output              x    output
#1     Stores     Ostues     EMMEMM      S|O , r|u     (.)..(.).. S|O , r|u
#2 University Unasersity MMEEMMMMMM      i|a , v|s ..(.)(.)...... i|a , v|s
#3     Street     Straeq     MMMEME      e|a , t|q     ...(.).(.) e|a , t|q

数据：

    df <- data.frame ("Col1" = c("Stores","University","Street"), 
       "Col2" = c("Ostues", "Unasersity", "Straeq"), 
       "Position" = c("EMMEMM","MMEEMMMMMM", "MMMEME"), 
       "Desired Output" = c("S|O , r|u","i|a , v|s","e|a , t|q"))

从 R 中不同位置的字符串中提取字母

Extract letters from a string at different positions in R

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substr