Menu
Lets say I have a string "Hello." I want to see if this string contains a period:
text <- "Hello."
results <- grepl(".", text)
This returns results as TRUE, but it would return that as well if text is "Hello" without the period.
I'm confused, I can't find anything about this in the documentation and it only does this for the period.
Any ideas?
273
The grepl() stands for “grep logical”. In R it is a built-in function that searches for matches of a string or string vector. The grepl() method takes a pattern and data and returns TRUE if a string contains the pattern, otherwise FALSE.
Any character (except for the newline character) will be matched by a period in a regular expression; when you literally want a period in a regular expression you need to precede it with a backslash. Many times you'll need to express the idea of the beginning or end of a line or word in a regular expression.
The grep and grepl functions use regular expressions or literal values as patterns to conduct pattern matching on a character vector. The grep returns indices of matched items or matched items themselves while grepl returns a logical vector with TRUE to represent a match and FALSE otherwise.
The Difference Between \s and \s+ For example, expression X+ matches one or more X characters. Therefore, the regular expression \s matches a single whitespace character, while \s+ will match one or more whitespace characters.
See the differences with these examples
> grepl("\\.", "Hello.")
[1] TRUE
> grepl("\\.", "Hello")
[1] FALSE
the . means anything as pointed out by SimonO101, if you want to look for an explicit . then you have to skip it by using \\. which means look for a .
R documentation is extensive on regular expressions, you can also take a look at this link to understand the use of the dot.
187
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
