title: replace word in character sentence in R
body: <p>Ok so, how do I change a word in a character vector of length 1?
  To be more specific, I have the sentence &quot;I want this book&quot; in a character vector of length 1 apparently, and I want to replace the word &quot;this&quot; with &quot;that&quot; and then find how many words &quot;that&quot; exist in the sentence (which ofc will be 1).
  Questions;
  How do I do this?
  Do I have to change something in the vector to use another code? Like make each word a unique character?
  I want to do this with the simplest possible way, avoiding perplexed coding if it shall be possible...
  Thank you all!</p>