Function substr()
The substr() function in R is used to extract or replace substrings from a character string. It allows you to specify the starting and ending positions of the substring you want to extract or replace.
Syntax
substr(x, start, stop)
Arguments:
- x:
- The character string or vector of strings from which to extract or replace the substring.
- Example: “Hello World”, c(“abc”, “def”).
- start:
- The starting position (1-based index) of the substring you want to extract or replace.
- Example: 1 for the beginning of the string.
- stop:
- The ending position (1-based index) of the substring you want to extract or replace.
- Example: 5 to end the substring at the fifth character.
Practical Examples
Example 1: Extracting a Substring
# Extract a substring from position 1 to 5
substr("Hello World", start = 1, stop = 5)
# [1] "Hello"
Example 2: Extracting from a Vector of Strings
# Extract a substring from position 2 to 4 for each element in a vector
substr(c("abcdef", "123456"), start = 2, stop = 4)
# [1] "bcd" "234"
Example 3: Replacing a Substring
# Replace substring "World" with "R" in "Hello World" s <- "Hello World" substr(s, start = 7, stop = 11) <- "R" # [1] "Hello R"
Example 4: Handling Edge Cases
# Extract a substring with start greater than stop
substr("Hello", start = 5, stop = 2)
# [1] ""
# Extract a substring with positions outside the string's range
substr("Hi", start = 1, stop = 10)
# [1] "Hi"
Points to Note
- 1-Based Indexing: start and stop indices are 1-based, meaning the first character of the string is at position 1.
- Empty Strings: If start is greater than stop, or if start or stop are outside the string’s range, the result is an empty string.
- Vectorized Operation: substr() works with character vectors. If x is a vector, start, and stop should be of the same length as x, or be length 1 to apply to all elements.
- Replacement: When using substr() to replace part of a string, ensure that the replacement string is of the same length as the substring being replaced.
Examples of Edge Cases
# Substring start and stop out of bounds
substr("example", start = 10, stop = 15)
# [1] ""
# Start greater than stop
substr("example", start = 5, stop = 2)
# [1] ""