title: How is.integer() works in R
body: <p>I have a data frame of numerics,integers and string. I would like to check which columns are integers and I do</p>
  
  <pre><code>raw&lt;-read.csv('./rawcorpus.csv',head=F)
  ints&lt;-sapply(raw,is.integer)
  </code></pre>
  
  <p>anyway this gives me all false. So I have to make a little change</p>
  
  <pre><code>nums&lt;-sapply(raw,is.numeric)
  ints2&lt;-sapply(raw[,nums],function(col){return(!(sum(col%%1)==0))})
  </code></pre>
  
  <p>The second case works fine. My question is: what is actually checking the 'is.integer' function? </p>