R grep() function - pattern matching and searching
R language examplesR grep() function is used to search a character vector for positions or values that match a specified pattern.
grepl() is its logical version, returning TRUE/FALSE. Both support regular expressions.
The syntax of the grep() function is as follows:
grep(pattern, x, value = FALSE, ignore.case = FALSE) grepl(pattern, x, ignore.case = FALSE)
Parameter description:
patternThe pattern to match (supports regular expressions).
xInput character vector.
valueWhether to return the matched value (TRUE) instead of just the index (FALSE). Default is FALSE.
ignore.caseWhether to ignore case.
Example
fruits <- c("apple", "banana", "orange", "grape", "pineapple", "mango")
# grep: return indices containing "ap"
print("Indices containing 'ap':")
print(grep("ap", fruits))
# grep with value: return matched values
print("Fruits containing 'ap':")
print(grep("ap", fruits, value = TRUE))
# grepl: return logical vector
print("Whether it contains 'ap':")
print(grepl("ap", fruits))
# grep: return indices containing "ap"
print("Indices containing 'ap':")
print(grep("ap", fruits))
# grep with value: return matched values
print("Fruits containing 'ap':")
print(grep("ap", fruits, value = TRUE))
# grepl: return logical vector
print("Whether it contains 'ap':")
print(grepl("ap", fruits))
Executing the above code produces the following result:
[1] "包含 'ap' 的索引:" [1] 1 4 5 [1] "包含 'ap' 的水果:" [1] "apple" "grape" "pineapple" [1] "是否包含 'ap':" [1] TRUE FALSE FALSE TRUE TRUE FALSE
grepl() combined with logical indexing can filter rows in a data frame:
Example
# User data with email addresses
df <- data.frame(
Name= c("Zhang San", "Li Si", "Wang Wu", "Zhao Liu"),
Email= c("zhang@example.com", "li@gmail.com",
"wang@example.com", "zhao@yahoo.com"),
stringsAsFactors = FALSE
)
# Filter users with example emails
example_users <- df[grepl("example", df$Email), ]
print("example email users:")
print(example_users)
df <- data.frame(
Name= c("Zhang San", "Li Si", "Wang Wu", "Zhao Liu"),
Email= c("zhang@example.com", "li@gmail.com",
"wang@example.com", "zhao@yahoo.com"),
stringsAsFactors = FALSE
)
# Filter users with example emails
example_users <- df[grepl("example", df$Email), ]
print("example email users:")
print(example_users)
Executing the above code produces the following result:
[1] "example 邮箱的用户:" 姓名 邮箱 1 张三 zhang@example.com 3 王五 wang@example.comOther extensions