title: How to replace all NA in a dataframe using tidyr::replace_na?
body: <p>I'm trying to fill all NAs in my data with 0's. Does anyone know how to do that using replace_na from tidyr? From documentation, we can easily replace NA's in different columns with different values. But how to replace all of them with some value? I have many columns...  </p>
  
  <p>Using mtcars dataset as an example:</p>
  
  <pre><code>mtcars [sample(1:nrow(mtcars), 4), sample(1:ncol(mtcars), 4)]&lt;- NA
  mtcars %&gt;% replace_na( ??? )
  </code></pre>