title: How to replace monthly with yearly values?
body: <p>I have a dataframe df as follows (my real data there are many columns):</p>
  <pre><code>  df &lt;- read.table(text = &quot;date    hfgf    lmo
         2019-01-01        0.7         1.4
         2019-02-01        0.11        2.3
         2019-03-01       1.22        6.7
         2020-04-01        0.44        5.2
         2020-05-01        0.19        2.3
         2021-06-01        3.97        9.5
         ,
               header = TRUE, stringsAsFactors = FALSE)
  </code></pre>
  <p>I would like to replace the monthly values in the columns value 1  value 2  etc   by the yearly mean.</p>
  <p>Note that I can melt and use summarize function but I need to keep the columns as they are.</p>