# Regular Expressions¶

Regular expressions is a general term which covers the idea of pattern searching, typically in a string (or a vector of strings).

For now we'll learn about two useful functions for regular expressions and pattern searching (we'll go deeper into this topic in general later on):

- grepl(), which returns a logical indicating if the pattern was found

- grep(), which returns a vector of index locations of matching pattern instances

For both of these functions you'll pass in a pattern and then the object you want to search. Let's see some quick examples:

In [1]:

    text <- "Hi there, do you know who you are voting for?"

In [4]:

    grepl('voting',text)

Out[4]:
TRUE
In [5]:

    grepl('Hi',text)

Out[5]:
TRUE
In [6]:

    grepl('Sammy',text)

Out[6]:
FALSE
In [8]:

    v <- c('a','b','c','d')

In [9]:

    grep('a',v)

Out[9]:
1
In [10]:

    grep('c',v)

Out[10]:
3

We'll learn more regular expression functions as we need them when doing exercises or projects. Want more info on regular expressions with R in the meantime? Check out this link