title: Problem dividing column of data.frame with a constant (object of type 'closure' is not subsettable)
body: <p>I do not understand why R is unable to divide <code>mydata$timestamp</code>. Even if I try to divide by <code>n</code> which went ok with <code>mydata$y</code>, it blows up. Maybe it is related to the integer/numeric difference, but why is this difference there and how do I fix it in my example?</p>
  
  <pre><code>mydata &lt;- read.csv(file="myfile.txt"))
  &gt; str(mydata)
  'data.frame':   687 obs. of  4 variables:
   $ timestamp: int  8 32 55 78 102 149 196 219 243 266 ...
   $ x        : int  -45 -46 -45 -43 -43 -41 -44 -43 -43 -44 ...
   $ y        : int  -190 -188 -189 -190 -188 -190 -186 -191 -190 -188 ...
   $ z        : int  -194 -192 -195 -194 -193 -197 -193 -193 -194 -196 ...
  &gt; head(mydata)
    timestamp   x    y    z
  1         8 -45 -190 -194
  </code></pre>
  
  <p>...</p>
  
  <pre><code>6       149 -41 -190 -197
  &gt;   x_resolution &lt;- 1000 # milliseconds
  &gt;   n = sqrt(mydata$x^2 + mydata$y^2 + mydata$z^2)
  &gt;   mydata$x &lt;- mydata$x / n
  &gt;   mydata$y &lt;- mydata$y / n
  &gt;   mydata$z &lt;- mydata$z / n
  &gt;   mydata$timestamp &lt;- data$timestamp / x_resolution
  Error in data$timestamp : object of type 'closure' is not subsettable
  &gt;   mydata$timestamp &lt;- data$timestamp / n
  Error in data$timestamp : object of type 'closure' is not subsettable
  &gt; str(n)
   num [1:687] 275 273 275 275 273 ...
  &gt; class(n)
  [1] "numeric"
  &gt; str(mydata$timestamp)
   int [1:687] 8 32 55 78 102 149 196 219 243 266 ...
  &gt; class(mydata$timestamp)
  [1] "integer"
  &gt; str(mydata$y)
   num [1:687] -0.69 -0.69 -0.687 -0.691 -0.689 ...
  &gt; class(mydata$y)
  [1] "numeric"
  &gt; 
  </code></pre>