Dealing with regular expressions

Regular expressions let you easily perform string manipulation with the help of just a handful of characters. In this recipe, we will look for digits, punctuation, and uppercase and lowercase in a vector of strings.

How to do it...

1. Define a test vector that you can search with regular expressions:

   test_string <- c("012","345",";.","kdj","KSR" ,"\n")
   

2. Look for digits:

   grep("[[:digit:]]",test_string, value = TRUE)
   which will result in :
   [1] "012" "345"
   

3. Look for punctuation:

   grep("[[:punct:]]",test_string, value = TRUE)
   which will have as a result
   [1] ";."
   

4. Look for lowercase letters:

   grep("[[:lower:]]",test_string, value = TRUE)
   

   Which will select the following:

   [1] "kdj"
   

5. Look for uppercase letters:

         grep("[[:upper:]]",test_string, value = TRUE)
   

   Which will select only upper cases:

        [1] "KSR"