R语言中创建支持可选引号的二元运算符%&%的实现问题

To create a binary operator %&% that concatenates two strings with a space—whether the inputs are quoted or unquoted—we need to use non-standard evaluation (NSE) to capture the literal text of each argument, regardless of whether it's wrapped in quotes.

Step-by-Step Implementation: #

1. Capture unevaluated arguments: Use substitute() to get the raw expression of each input (this preserves both quoted strings and unquoted symbols).
2. Convert to character: Use as.character() to turn both symbols and quoted strings into plain text strings.
3. Concatenate with space: Use paste() to combine the two strings with a single space separator.

Final Code: #

`%&%` <- function(a, b) {
  # Capture the literal input text for each argument
  a_text <- as.character(substitute(a))
  b_text <- as.character(substitute(b))
  
  # Concatenate with a space
  paste(a_text, b_text)
}

Testing the Operator: #

Let's verify it works for both quoted and unquoted inputs:

# Unquoted arguments
Hello %&% World
# Output: [1] "Hello World"

# Quoted arguments
"Hello" %&% "World"
# Output: [1] "Hello World"

# Mixed quoted/unquoted
Hi %&% "there"
# Output: [1] "Hi there"

Key Notes: #

• This operator treats unquoted inputs as literal text, not variable names. Even if you don't have a variable named Hello, Hello %&% World will still return "Hello World".
• If you pass a variable (e.g., x <- "Hi"; x %&% World), it will use the variable's name ("x") instead of its value. This aligns with your requirement of treating quotes as optional for literal string inputs.

内容的提问来源于stack exchange，提问作者dataminingblues