regular expressions overview

tools for learning and applying regex functions

general:

regex functions allow for complex string ("Zeichenketten") searches within a text or textbundle.
simple: e.g. if you want to find all occurences of a name (speaker) in a play, you could search for (if the speaker is named "Paul"):
(Paul) In R the command would be:
m<-grep("Paul",textarray) where m will be the resulting array of occurences (indices) of "Paul" within a defined array of strings. if you have a text sample.txt of plain text consisting of several paragraphs (where the text is divided with CARRIAGE RETURN or by means of a header) the routine looks like this:

textarray<-readLines("sample.txt")
m<-grep("Paul",textarray)
print(textarray[m])

this will output only the textlines containing a Paul-instance.
you could if you want that make a Paula of all Pauls by:

textarray.modified<-gsub("Paul","Paula",textarray)
print(textarray.modified)

the regex methods allow very fine grained search&replace commands, see the learning tools above where you can experiment with search formula in a app or browser.