title: How to apply a function on a selection of columns in a pipe sequence in R?
body: <p>I have a dataframe (or a tibble no matter) with many columns and I want to apply a function (let's say rowSums) on only 7 of them, but I don't want to get reed of the others. The trick is that I want to do so in a pipe sequence 
  - create (or read the data)
  - apply the function
  - optional operation after that</p>
  
  <p>Here is a reproductible exemple on a dataframe where I would like to rowSums on the first 3 columns</p>
  
  <pre><code>data &lt;- data.frame("v1" = runif(10, 0, 10), "v2" = runif(10, 0 ,10), "v3" = runif(10, 0 ,10), "v4" = rep("some_charchter", 10))
  </code></pre>
  
  <p>the way I would usually do it  is </p>
  
  <pre><code>data$sum &lt;- rowSums(data[,1:3])
  </code></pre>
  
  <p>but I want something like this</p>
  
  <pre><code>data &lt;- data.frame("v1" = runif(10, 0, 10), "v2" = runif(10, 0 ,10), "v3" = runif(10, 0 ,10), "v4" = rep("some_charchter", 10)) %&gt;% 
    mutate(sum = rowSums())
  
  </code></pre>
  
  <p>Thanks for your help !</p>