title: Create a stack of n subset data frames from a single data frame based on date column
body: <p>I need to create a bunch of subset data frames out of a single big <code>df</code>, based on a date column (e.g. - "Aug 2015" in month-Year format). It should be something similar to the subset function, except that the count of subset dfs to be formed should change dynamically depending upon the available values on date column</p>
  
  <p>All the subsets data frames need to have similar structure, such that the date column value will be one and same for each and every subset <code>df</code>.</p>
  
  <p>Suppose, If my big <code>df</code> currently has last 10 months of data, I need 10 subset data frames now, and 11 dfs if i run the same command next month (with 11 months of base data). </p>
  
  <p>I have tried something like below. but after each  iteration, the subset <code>subdf_i</code> is getting overwritten. Thus, I am getting only one subset df atlast, which is having the last value of month column in it. </p>
  
  <p>I thought that would be created as 45 subset dfs like <code>subdf_1</code>, <code>subdf_2</code>,... and <code>subdf_45</code> for all the 45 unique values of month column correspondingly.</p>
  
  <pre><code>uniqmnth &lt;- unique(df$mnth)
  
  for (i in 1:length(uniqmnth)){
  
      subdf_i &lt;- subset(df, mnth == uniqmnth[i])
  
      i==i+1
  
  }
  </code></pre>
  
  <p>I hope there should be some option in the subset function or any looping might do. I am a beginner in R, not sure how to arrive at this. </p>