![]() ![]() R contains a set of functions in the base package that we can use to find pattern matches. # match states that contain z grep ( pattern = "z+", state.name, value = TRUE ) # "Arizona" # match states with two s grep ( pattern = "s", state.name, value = TRUE ) # "Alaska" "Arkansas" "Illinois" "Kansas" # "Louisiana" "Massachusetts" "Minnesota" "Mississippi" # "Missouri" "Nebraska" "New Hampshire" "New Jersey" # "Pennsylvania" "Rhode Island" "Tennessee" "Texas" # "Washington" "West Virginia" "Wisconsin" ![]() For information on the grep function used in this example visit the main regex functions section. The following provides examples to show how to use the anchor syntax to match character classes. The following displays the general syntax for common character classes but these can be altered easily as shown in the examples that follow: In addition, to match any characters not in a specified character set we can include the caret ^ at the beginning of the set within the brackets. To match one of several characters in a specified set we can enclose the characters of concern with square brackets. # substitute any digit with an underscore gsub ( pattern = "\\d", "_", "I'm working in RStudio v.0.99.484" ) # "I'm working in RStudio v._._._" # substitute any non-digit with an underscore gsub ( pattern = "\\D", "_", "I'm working in RStudio v.0.99.484" ) # "_0_99_484" # substitute any whitespace with underscore gsub ( pattern = "\\s", "_", "I'm working in RStudio v.0.99.484" ) # "I'm_working_in_RStudio_v.0.99.484" # substitute any wording with underscore gsub ( pattern = "\\w", "_", "I'm working in RStudio v.0.99.484" ) # "_'_ _ _ _ _._._._" Character classes ![]() For information on the sub and gsub functions used in this example visit the main regex functions section. The following provides examples to show how to use the escape syntax to find and replace metacharacters. The following displays the general escape syntax for the most common metacharacters: To match metacharacters in R you need to escape them with a double backslash “\\”. Metacharacters consist of non-alphanumeric symbols such as: To read more about the specifications and technicalities of regex in R you can find help at help(regex) or help(regexp). This section will provide you with the basic foundation of regex syntax however, realize that there is a plethora of resources available that will give you far more detailed, and advanced, knowledge of regex syntax. Then I cover the functions provided in base R and in the stringr package you can apply to identify, extract, replace, and split parts of character strings based on the regex pattern specified.Īt first glance (and second, third,…) the regex syntax can appear quite confusing. This will provide you with the basic understanding of the syntax required to establish the pattern to find. First, I cover the syntax that allow you to perform pattern matching functions with meta characters, character and POSIX classes, and quantifiers. In this section, we will cover both of these aspects. The other has to do with the functions used for regex matching in R. One has to do with the syntax, or the way regex patterns are expressed in R. To understand how to work with regular expressions in R, we need to consider two primary features of regular expressions. The pattern can also be as simple as a single character or it can be more complex and include several characters. ![]() Typically, regex patterns consist of a combination of alphanumeric characters as well as special characters. A regular expression (aka regex) is a sequence of characters that define a search pattern, mainly for use in pattern matching with text strings. ![]()
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