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Replace the character column of dataframe in R

by Charles James

The following example updates all instances of Portola Pkwy with Orange St on all columns of R DataFrame. Using some of the approaches explained in this article, you can also replace NA with Empty String in R dataframe. Let’s create an R DataFrame and explore examples and output. Either a character vector, or something coercible to one. String_expr2 is the pattern string, or the string expression to find within the first expression and is expressed as CHAR, VARCHAR, UNICHAR, UNIVARCHAR, VARBINARY, or BINARY data type.

The third input box on the screen corresponds to what you would type into the replacement argument of the str_replace() function, and the results are presented below. The middle input box on the screen corresponds to what you would type into the string argument of the str_replace() function. The top input box on the screen corresponds to what you would type into the pattern argument of the str_replace() function. First, you can use the regex tester without logging in. However, I typically do log in because that allows me to save regular expressions and use them again later. We used stringr’s str_extract() function pull the last name out of the full name “zariah hernandez”.

The following example replaces string St with Street on column address. But if “.” matches any character, how do you match the character “.”? You need to use an “escape” to tell the regular expression you want to match it exactly, not use its special behaviour. Like strings, regexps use the backslash, \, to escape special behaviour.

Note that this does not replace strings that become part of replacement strings. This may be a problem when you want to remove multiple instances of the same repetative pattern, several times in a row. To replace the character column of dataframe in R, we use str_replace() function of “stringr” package.

To learn regular expressions, we’ll use str_view() and str_view_all(). These functions take a character vector and a regular expression, and show you how they match. We’ll start with very simple regular expressions and then gradually get more and more complicated.

The first word character at the end of the string is “z”, then “e”, then “dnanreh”. It tells the str_extract() function to look for the pattern at the end of the string only. Let’s go ahead and use it to remove “city of” from the values in the address_city column now.

When you first look at a regexp, you’ll think a cat walked across your keyboard, but as your understanding improves they will soon start to make sense. R has a very powerful set of features for building and using regular expressions. In this episode we move beyond the basics and discuss anchors, universal charlotte beer festivals 2016 and specific metacharacters, and how to specify groups within a pattern that you can use in the replacement value. Finally, we’ll use all this with the separate function. We’ll do all this in RStudio using the stringr package. This function can be used on both DataFrame columns and a vector.

Another common task that I perform on character strings is to separate the strings into multiple parts. For example, sometimes we may want to separate full names into two columns. To complete this task, we will once again use regular expressions.

Since these methods are used on vector, let’s create a R vector and replace values in it with pattern matching. Since every column in a DataFrame is a vector, you can also use pattern matching on DataFrame columns. In order to use this str_replace() method, first, you need to load its library using library(“stringr”). In case you don’t have this package, install it using install.packages(“stringr”). The stringr package provides a set of functions to work with strings as easily as possible. We used stringr’s str_detect() function create three new dummy variables in our data frame.

We also learned how to coerce character vectors to factor vectors that we can use for categorical data analysis. However, up to this point, we haven’t done a lot of manipulation of the values stored inside of the character strings themselves. Sometimes, however, we will need to manipulate the character string before we can complete other data management tasks or analysis. Some common examples from my projects include separating character strings into multiple parts and creating dummy variables from character strings that can take multiple values.

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