title: specify the first day of a 3 months period (to plot a line plot)
body: <p>my data look like</p>
  <pre><code>&gt; keep_long_format
            Date              Injury.Cause  n
  1   2019-03-25         Falls from height  1
  2   2019-03-25     Falls on level ground  3
  3   2019-03-25    Road traffic accidents  3
  4   2019-03-26    Road traffic accidents  5
  5   2019-03-27     Falls on level ground  3
  6   2019-03-27    Road traffic accidents  3
  7   2019-03-28     Falls on level ground  2
  8   2019-03-28    Road traffic accidents  3
  9   2019-03-29     Falls on level ground  4
  10  2019-03-29    Road traffic accidents  9
  11  2019-03-30         Falls from height  2
  12  2019-03-30     Falls on level ground  2
  13  2019-03-30    Road traffic accidents  7
  14  2019-03-31     Falls on level ground  1
  15  2019-03-31    Road traffic accidents  1
  16  2019-04-01     Falls on level ground  3
  17  2019-04-02 Assaults related injuries  1
  18  2019-04-02     Falls on level ground  1
  19  2019-04-02    Road traffic accidents  2
  20  2019-04-03         Falls from height  2
  21  2019-04-03    Road traffic accidents  4
  22  2019-04-04         Falls from height  2
  23  2019-04-04     Falls on level ground  2
  24  2019-04-04    Road traffic accidents  6
  </code></pre>
  <p>I want to plot these data on line plot and show data of each three months.</p>
  <p>This is what I did</p>
  <pre><code>keep_long_format &lt;- keep_long_format %&gt;% mutate(Trimonthly = round_date(Date, unit = &quot;3 months&quot; )) 
  
  
  
  Pivot.Trimonthly &lt;- keep_long_format %&gt;%
    group_by(Trimonthly, Injury.Cause ) %&gt;%
    summarise(Trimonthly.sum = sum(n))
  </code></pre>
  <p>the problem is that cases during the 5 days before 2019-4-1 are considered as a separate 3 months and looks very low (of course as it reflects 5 days compared to the three months data points on the plot)</p>
  <p>How can I make the 3 months start from 2019-3-25 to 2019-6-24 (and then, the next 3 months start from 2019-6-25 ...etc)</p>
  <p>thank you in advance</p>