title: How to get rowSums for selected columns in R
body: <p>I am a newbie to R and seek help to calculate sums of selected column for each row. My simple data frame is as below. </p>
  
  <pre><code>data = data.frame(location = c("a","b","c","d"),
              v1 = c(3,4,3,3), v2 = c(4,56,3,88), v3 =c(7,6,2,9), v4=c(7,6,1,9),
              v5 =c(4,4,7,9), v6 = c(2,8,4,6))
  </code></pre>
  
  <p>I want sum of columns V1 to V3 and V4 to V6 for my each row in a new data frame.</p>
  
  <pre><code>   x1   x2
  a  14   13   
  b  66   18
  c
  d
  </code></pre>
  
  <p>I did something like below. </p>
  
  <pre><code>rowSums(data[,2:4][,5:7])
  </code></pre>
  
  <p>But something should be wrong in my codes. Thanks in advance for any help.</p>