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I have a character vector containing variable names such as x <- c("AB.38.2", "GF.40.4", "ABC.34.2"). I want to extract the letters so that I have a character vector now containing only the letters e.g. c("AB", "GF", "ABC").
Because the number of letters varies, I cannot use substring to specify the first and last characters.
How can I go about this?
748
The substring function in R can be used either to extract parts of character strings, or to change the values of parts of character strings. substring of a vector or column in R can be extracted using substr() function. To extract the substring of the column in R we use functions like substr() and substring().
To get access to the individual characters in an R string, you need to use the substr function: str = 'string' substr(str, 1, 1) # This evaluates to 's'. For the same reason, you can't use length to find the number of characters in a string. You have to use nchar instead.
The substr() method extracts a part of a string. The substr() method begins at a specified position, and returns a specified number of characters. The substr() method does not change the original string. To extract characters from the end of the string, use a negative start position.
To split a string in R, use the strsplit() method. The strsplit() is a built-in R function that splits the string vector into sub-strings. The strsplit() method returns the list, where each list item resembles the item of input that has been split.
you can try
sub("^([[:alpha:]]*).*", "\\1", x)
[1] "AB" "GF" "ABC"
The previous answers seem more complicated than necessary. This question regarding digits also works with letters:
> x <- c("AB.38.2", "GF.40.4", "ABC.34.2", "A B ..C 312, Fd", " a")
> gsub("[^a-zA-Z]", "", x)
[1] "AB" "GF" "ABC" "ABCFd" "a"
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