title: Julia: How to create a new column in DataFrames.jl by adding two columns using `transform` or `@transform`?
body: <pre><code>using DataFrames
  
  df = DataFrame(a=1:3, b=1:3)
  
  </code></pre>
  <p>How do I create a new column <code>c</code> such that <code>c = a+b</code> element wise?</p>
  <p>Can't figure it out by reading the <code>transform</code> doc.</p>
  <p>I know that</p>
  <p><code>df[!, :c] = df.a .+ df.b</code></p>
  <p>works but I want to use <code>transform</code> in a chain like this</p>
  <pre><code>@chain df begin
    @transform(c = :a .+ :b)
    @where(...)
    groupby(...)
  end
  </code></pre>
  <p>The above syntax doesn't work with DataFramesMeta.jl</p>