title: How to succinctly write a formula with many variables from a data frame?
body: <p>Suppose I have a response variable and a data containing three covariates (as a toy example):</p>
  
  <pre><code>y = c(1,4,6)
  d = data.frame(x1 = c(4,-1,3), x2 = c(3,9,8), x3 = c(4,-4,-2))
  </code></pre>
  
  <p>I want to fit a linear regression to the data:</p>
  
  <pre><code>fit = lm(y ~ d$x1 + d$x2 + d$y2)
  </code></pre>
  
  <p>Is there a way to write the formula, so that I don't have to write out each individual covariate? For example, something like</p>
  
  <pre><code>fit = lm(y ~ d)
  </code></pre>
  
  <p>(I want each variable in the data frame to be a covariate.) I'm asking because I actually have 50 variables in my data frame, so I want to avoid writing out <code>x1 + x2 + x3 + etc</code>.</p>