title: Add new variable with for loop and if statements in R
body: <p>Let's assume I have a data set with 2 variables, a and b, where all b's are a's, but not all a's are b's. </p>
  
  <pre><code>a&lt;-rbind(1,1,1,1,1)
  b&lt;-rbind(0,0,0,1,1)
  d&lt;-cbind(a,b)
  d
        [,1] [,2]
  [1,]    1    0
  [2,]    1    0
  [3,]    1    0
  [4,]    1    1
  [5,]    1    1
  </code></pre>
  
  <p>I want to create a new third variable to condense this information into a single data frame. I attempted to do so by writing a loop for 1 in nrows, if the a variable is 1 then write a 2, and if the b variable is 1 then write a 1</p>
  
  <pre><code>e&lt;- for (i in 1:nrow(d)) {
      if (d[,1]==1) {
          e$new[,i] &lt;- 2
      } # end if 1
      else (d[,2]==1)
      e$new[,i]&lt;-1
          } # end for 2
  
  } # end for
  </code></pre>
  
  <p>I basically want the output to look as such:</p>
  
  <pre><code>&gt; d
         [,1] [,2] [,3]
   [1,]    1    0    2
   [2,]    1    0    2
   [3,]    1    0    2
   [4,]    1    1    1
   [5,]    1    1    1
  </code></pre>
  
  <p>I keep getting an error: Error in e$new[, i] &lt;- 0 : incorrect number of subscripts on matrix
  In addition: Warning messages:
  1: In 1:x : numerical expression has 2 elements: only the first used
  2: In if (d[, 1] == 1) { :
    the condition has length > 1 and only the first element will be used</p>
  
  <p>Any help debugging the script would be appreciated! </p>