R语言：查找字符列表中含特定字符串元素的位置

Got it, let's fix this for you! The issue with match() and str_locate() is that they don't do what you need here:

• match() looks for exact matches of your target string (it would only find an element that's exactly "Belgium", which doesn't exist in your list)
• str_locate() returns the position of the string inside each element, not the index of the element in the list

Instead, use grep()—it's designed to find elements in a character vector that contain a specific substring, and returns their indices directly.

Step 1: Define the Function #

Here's a simple function that takes your character list and target string, then returns the position(s) of elements containing that string:

find_element_position <- function(char_list, target) {
  # grep returns indices of elements that contain the target substring
  grep(target, char_list)
}

Step 2: Test It with Your Data #

Using your list_April example:

# Test with "Belgium"
find_element_position(list_April, "Belgium")
# Output: [1] 7

# Test another country, like "United States"
find_element_position(list_April, "United States")
# Output: [1] 19

Alternative: Using grepl() + which() #

If you prefer a more explicit approach, you can combine grepl() (which returns a logical vector indicating matches) with which() (which converts logicals to indices):

find_element_position <- function(char_list, target) {
  which(grepl(target, char_list))
}

This works exactly the same way as the grep version—just a different syntax.

Why Your Previous Attempts Didn't Work #

• match("Belgium", list_April) returns NA because none of the elements are exactly "Belgium" (all have extra numbers/text)
• str_locate(list_April, "Belgium") returns a matrix showing where "Belgium" starts/ends in each element, not the element's position in the list

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