title: Conditional subtraction in R data frame
body: <p>I have a fairly straightforward need, but I can't find a previously asked question that is similar enough. I've been trying with dplyr, but can't figure it out.</p>
  <pre><code> julian year
     088   22
     049   19
     041   22
     105   18
     125   22
     245   20
  </code></pre>
  <p>What I want is for each value where data$julian &lt; 105, subtract '1' from data$year, so that</p>
  <pre><code> julian year
     088   21
     049   18
     041   21
     105   18
     125   22
     245   20
  </code></pre>