grepl for a period "." in R?

r regex grepl
marc picture marc · Oct 24, 2013 · Viewed 14.8k times · Source

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?

Answer

Jilber Urbina picture Jilber Urbina · Oct 24, 2013

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.

Related questions

grepl in R to find matches to any of a list of character strings

Is it possible to use a grepl argument when referring to a list of values, maybe using the %in% operator? I want to take the data below and if the animal name has "dog" or "cat" in it, I want …

Read More
Use grepl to search either of multiple substrings in a text

I am using grepl() in R to search if either of the following genres exist in my text. I am doing it like this right now: grepl("Action", my_text) | grepl("Adventure", my_text) | grepl("Animation", my_text) | grepl("Biography", …

Read More
Complete word matching using grepl in R

Consider the following example: > testLines <- c("I don't want to match this","This is what I want to match") > grepl('is',testLines) > [1] TRUE TRUE What I want, though, is to only match 'is' when it …

Read More