Making regex examples work for you!
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One of the most frequently used string recognition algorithms out there is regex and R implements regex. However, users can often be frustrated with how despite taking examples verbatim from many sources such as stackoverflow they do not seem to work. From my own experience, I have found that the largest issue is really about what characters need to be escaped from R.Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.
For example:
Listing all files whose names match a simple pattern.
Looking at “/^.*icon.*\.png$/i” from
I was able to get “^.*icon.*.png$“ to work in R though I lost the case insensitivity. I think including the “^.” ensures that only files in the current directory, not subdirectory are matched but I am not sure.
list.files(“C:/Clipart/”, pattern=”^.*icon.*.png$”)
[1] “manicon.png” “handicon.png” “bookicon.png”
Looking at the original entry we can see that what was causing us problems was the attempt to escape the “^” which does not need to be escaped in R.
Before looking at another example lets modify the previous command slightly to show how we can make it match differently.
list.files(“C:/Clipart/”, pattern=”^.*icon*.*.png$”)
[1] “manicon.png” “handicon.png” “bookicon.png” “iconnew.png”
There are a lot of resources available for regex since it is really its own text matching language supported by many different programming languages. A good introductory guide can be found:
or
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