Catching errors when using tolower
Posted on May 29, 2012
When I’m working in R with text data parsed from online opinion forums and social webs (e.g. twitter), I need to do some cleaning and pre-processing such as removing punctuation marks, striping extra white spaces, or converting text to lower case.
More often than not, when using the tolower()
function I encounter myself with a really annoying error that is a truly pain in the butt.
Consider the following example. Let’s say we have the text from a tweet in an object
called some_text. When we print the object in the console, we get a warning message
(in red) like this:
So, how can we solve this error? Meet the tryCatch
function! This function will help us to catch possible errors. We’ll make a new function
combining tryCatch() and tolower() so we can identify any undesirable text
without returning any ugly message and without stopping our programs.
Here’s my tryTolower() function
tryTolower = function(x)
{
# create missing value
# this is where the returned value will be
y = NA
# tryCatch error
try_error = tryCatch(tolower(x), error = function(e) e)
# if not an error
if (!inherits(try_error, "error"))
y = tolower(x)
return(y)
}Let’s test it
Suppose you have a character vector with five elements
# vector with text
text_vector = c(
"Motivation, philosophy and technique in activism. #Assange and #Occupy: http://t.co/89PFkyjh via @RT_com",
"No work today, slept through the classes I wanted at the gym. Now I need to find something to occupy my time \ud83d\udc4d\ud83d\ude09",
"RT @jdavis4100: The Spirit of God and fear never occupy the same space. The presence of one automatically implies the absence of the other...",
"Police given powers to enter homes http://t.co/VXmtfPV5 and tear down anti- #Olympics posters during Games #Occupy #Anonymous #wakeup #fb",
"RT @OccupyWallSt: RT @WSOASP12: I quit my job to join the occupy movement. Time to stand up and speak out, I'm not here to make another man rich @Occupy #OWS")
# apply tolower (you should get an error message)
tolower(text_vector)
# now apply tryTolower with sapply
# (you should get a missing value when tryTolower finds an error)
sapply(text_vector, function(x) tryTolower(x))