如何在R语言中查找一个向量在另一个向量中的首次出现位置？

Great question! You're right that which() and match() only handle single-element matches—they don't work for finding a contiguous sequence of elements like your x1 in x2.

R's base package doesn't have a built-in function specifically for this exact task, but it's straightforward to build your own, or use functions from third-party packages if you prefer. Here are a couple of approaches:

1. Custom Function (Base R, No Packages Needed) #

This function checks every valid starting position in x2 where x1 could fit, and returns the first match it finds:

find_first_sequence_match <- function(pattern, text) {
  pattern_len <- length(pattern)
  text_len <- length(text)
  
  # Calculate all valid starting positions (avoids going out of bounds)
  possible_starts <- seq_len(text_len - pattern_len + 1)
  
  # Loop through each position to check for a full match
  for (start in possible_starts) {
    window <- text[start:(start + pattern_len - 1)]
    if (all(window == pattern)) {
      return(start)
    }
  }
  
  # Return NA if no match exists
  return(NA)
}

Test it with your example: #

x1 <- c(0,1,2)
x2 <- c(1,2,0,1,2,3,4,5,0,1,0,1,2)

find_first_sequence_match(x1, x2)
# Output: 3

2. Using a Third-Party Package (zoo) #

If you don't mind using an external package, the rollapply() function from the zoo package creates sliding windows over x2 to check for matches:

library(zoo)

# Create sliding windows matching x1's length, check for full matches
matches <- rollapply(x2, length(x1), function(window) all(window == x1))

# Grab the first matching position
first_match_pos <- which(matches)[1]
first_match_pos
# Output: 3

Either approach will reliably return the first starting position of your target sequence.

内容的提问来源于stack exchange，提问作者Zofhd