Extract characters (substrings) from a string is very common in data cleaning. One may wish to store first names and surnames in separate columns, however, in the raw data both are stored in a single column. This is where extracting substrings come in to play.
There are various ways to extract characters and this post briefly describes two functions: substr() and substring().
substr()
Here’s how to use substr():
substr(x, start, stop)
where x is a character vector, start and stop take integer values as inputs to indicate the beginning and ending point.
Working example:
substr("Yukai Zou", 1, 5)
## [1] "Yukai"
substring()
This function is very similar to substr() but can do slightly more. Here’s how to use substring():
substring(x, first, last)
note that the 2nd and 3rd attributes are named first and last, to distinguish from substr(). What’s different here is that integer vector can be taken as input, and substring() will try to figure out the rest to slice the string for you.
To illustrate that, let’s take a closer look at the same example:
substring("Yukai Zou", 1:5, 1:5)
## [1] "Y" "u" "k" "a" "i"
Here, a vector “1,2,3,4,5” (1:5) was passed to both the first and last attributes, and substring() took each of the elements one by one, meaning that it started and ended at the 1st element ("Y"), then the 2nd ("u"), then the 3rd ("k") … As a result, the output is a character vector that breaks the first name into single characters.
See also: The use of grepl(), Notes on string editing