I have a question regarding to extract letters from a string For example I have in R one vector like:
America, Asia, Europe
I want to get all of the upper letters in this format like
AAE or A, A, E
How can I do this with regmatches and regexpr?
2 Answers
A simple gsub
x <- "America, Asia, Europe"
gsub("[^A-Z]","",x)
[1] "AAE"
4 Comments
Tim Biegeleisen
Your suggestion is overly simplified. What happens if a given word happens to have two capital letters, e.g. "South America"? Your suggestion would leave behind
SA, which might not be what the OP wants here. Always consider giving a flexible solution.
Abcxyz
is it also possible to check if for example the letter A is then inside the new expression e.g AAE ?
Daniel O
@Abcxyz yes, you can use
grepl("A", x) to check.Daniel O
@TimBiegeleisen, OP asked to extract all capital letters. What if OP wants all the capital letters? in that case "South America" would return
SA and that would be exactly what OP asked for.You could use gsub here:
x <- "America, Asia, Europe"
output <- gsub("\\b([A-Z])[a-z]+(?:,\\s*)?", "\\1", x)
output
[1] "AAE"
If you want a CSV string output of capital letters, then consider:
x <- "America, Asia, Europe"
output <- gsub("\\b([A-Z])[a-z]+(?:,\\s*)?", "\\1, ", x)
output <- sub(", $", "", output)
output
[1] "A, A, E"
answered Jun 30, 2020 at 17:05
4 Comments
Abcxyz
Thanks a lot! is it also possible to check if for example the letter A is then inside the new expression e.g AAE ?
Tim Biegeleisen
I don't understand your follow up question?
Abcxyz
For example if I want to check if the letter A appears in AAE or if the letter E appears in AAE
Tim Biegeleisen
Use:
grepl("A", "AAE", fixed=TRUE)
gsub("[a-z]+","",x)