title: R get index satisty the condition
body: <p>Given vector <code>x</code> as:</p>
  
  <pre><code>x = c(5, 7, 8, 9, 2, 3)
  </code></pre>
  
  <p>I want to get the index of x, which x value is bigger than 7</p>
  
  <p>The result I expect:</p>
  
  <pre><code>2, 3, 4
  </code></pre>
  
  <p>I have tried</p>
  
  <pre><code>Position[x &gt;= 7, x]
  </code></pre>
  
  <p>But I get the error:</p>
  
  <pre><code>Error in Position[x &gt;= 7, x] : 
    object of type 'closure' is not subsettable
  </code></pre>