Key Arguments:

• pattern: The regular expression or string to search for.
• x: The character vector to be searched.
• ignore.case: If TRUE, the case of the pattern and the string will be ignored.
• perl: If TRUE, Perl-compatible regex is used.
• fixed: If TRUE, pattern is a string to be matched as is.
• useBytes: If TRUE, matching is done byte-by-byte.

Practical Example

Imagine you have a list of phrases, and you want to find those that contain either “cat” or “dog”.

# Sample data
phrases <- c("The cat is sleeping", "A dog barked loudly", "The sun is shining", "Cats and dogs are pets", "Birds are chirping")

# Patterns to search
patterns <- c("cat", "dog")

# Combine patterns using OR operator
combined_pattern <- paste(patterns, collapse = "|")

# Use grepl to find matches
matches <- grepl(combined_pattern, phrases, ignore.case = TRUE)

# Show results
result <- phrases[matches]
print(result)

[1] "The cat is sleeping"    "A dog barked loudly"    "Cats and dogs are pets"

Explanation:

1. Data Preparation: We start with a vector phrases containing several sentences.
2. Pattern Combination: We combine our patterns into a single string using paste() with collapse = "|". This creates a regular expression "cat|dog", which grepl interprets as “find either ‘cat’ or ‘dog’”.
3. Search Operation: grepl is then used to search for the combined pattern within phrases. The argument ignore.case = TRUE ensures the search is case-insensitive.
4. Extract Matches: We use the result of grepl to subset the phrases vector, displaying only those elements that contain either “cat” or “dog”.