title: detect missings (NA or 0) in data frame
body: <p>i want to create a new variable in a data frame that contains information about the other variables.</p>
  
  <p>I have got a large data frame. To keep it short let's say:</p>
  
  <pre><code>a &lt;- c(1,0,2,3)
  b &lt;- c(3,0,1,1)
  c &lt;- c(2,0,2,2)
  d &lt;- c(4,1,1,1)
  
  (df &lt;- data.frame(a,b,c,d) )
  
    a b c d
  1 1 3 2 4
  2 0 0 0 1
  3 2 1 2 1
  4 3 1 2 1
  </code></pre>
  
  <p>Aim: Create a new variable that informs me if one person (row) has cero reports (or missings / NA) either in the variables a+b or in the variables c+d. </p>
  
  <pre><code>  a b c d  x
  1 1 3 2 4  1
  2 0 0 0 1 NA
  3 2 1 2 1  1
  4 3 1 2 1  1
  </code></pre>
  
  <p>As i have a large data frame i was thinking about the use of df[1:2] and df[3:4] so that i do not need to type every variable name. But i am not sure which is the best way to implement it. Maybe dplyr has a nice option?</p>