向 R 中的字符串向量添加字母

Question

忽略我的

input

中的主题标记行，有没有办法添加：

• A*

  在没有

  *

  前缀的“字母数字”元素之前，出现在

  ~

  和
之后

• R*

  在没有

  *

  前缀的“字母数字”元素之前并出现在

  ~~

  之后？

所需的

output

如下所示。

input <- "y ~ x1 + x2
           ## Variances of x1 and x2 are 1
           x1 ~~ 1*x1
           x2 ~~ 1*x2
           ## x1 and x2 are correlated
           x1 ~~ x2"

output <- "y ~ A*x1 + A*x2
           ## Variances of x1 and x2 are 1
           x1 ~~ 1*x1
           x2 ~~ 1*x2
           ## x1 and x2 are correlated
           x1 ~~ R*x2"

Answer 1

使用“gsub”：

   # Input string
input <- "y ~ x1 + x2
           ## Variances of x1 and x2 are 1
           x1 ~~ 1*x1
           x2 ~~ 1*x2
           ## x1 and x2 are correlated
           x1 ~~ x2"

# Function to add prefixes before alphanumeric elements based on patterns
addPrefixes <- function(input) {
  # Add "A*" before alphanumeric elements that don't have a * prefix and appear after ~
  output <- gsub("(?<=~ )([^*\\s]+)", "A*\\1", input, perl = TRUE)
  
  # Add "R*" before alphanumeric elements that don't have a * prefix and appear after ~~
  output <- gsub("(?<=~~ )([^*\\s]+)", "R*\\1", output, perl = TRUE)
  
  return(output)
}

output <- addPrefixes(input)
cat(output)