title: Data Manipulation, Looping to add columns
body: <p>I have asked this question a couple times without any help.  I have since improved the code so I am hoping somebody has some ideas!  I have a dataset full of 0's and 1's.  I simply want to add the 10 columns together resulting in 1 column with 3835 rows.  This is my code thus far: </p>
  
  <pre><code># select for valid IDs
  data = history[history$studyid %in% valid$studyid,]
  
  sibling = data[,c('b16aa','b16ba','b16ca','b16da','b16ea','b16fa','b16ga','b16ha','b16ia','b16ja')]
  
  # replace all NA values by 0
   sibling[is.na(sibling)] &lt;- 0
  
  # loop over all columns and count the number of 174
  apply(sibling, 2, function(x) sum(x==174))
  </code></pre>
  
  <p>The problem is this code adds together all the rows, I want to add together all the columns so I would result with 1 column.  This is the answer I am now getting which is wrong:</p>
  
  <pre><code>b16aa b16ba b16ca b16da b16ea b16fa b16ga b16ha b16ia b16ja 
     68    36    22    18     9     5     6     5     4     1 
  </code></pre>