title: How to identify the best frequency in a time series?
body: <p>I have a database metrics grouped by day, and I need to forecast the data for the next 3 months. These data have seasonality, (I believe that the seasonality is by days of the week).</p>
  
  <p>I want to use the Holt Winters method using R, I need to create a time series object, which asks for frequency, (That I think is 7). 
  But how can I know if I'm sure? Have a function to identify the best frequency?</p>
  
  <p>I'm using:</p>
  
  <pre><code>FID_TS &lt;- ts(FID_DataSet$Value, frequency=7)
  
  FID_TS_Observed &lt;- HoltWinters(FID_TS)
  </code></pre>
  
  <p>If I decompose this data with <code>decompose(FID_TS)</code>, I have:</p>
  
  <p><a href="https://i.stack.imgur.com/9zGSD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9zGSD.png" alt="enter image description here"></a></p>
  
  <p>And this is my first forecast <code>FID_TS_Observed</code>:</p>
  
  <p><a href="https://i.stack.imgur.com/V3ILQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/V3ILQ.png" alt="enter image description here"></a></p>
  
  <p>When I look at the history of the last year, they starts low in the first 3 months and increase from month 3 to 11, when they decrease again. </p>
  
  <p>Maybe my daily data, have a daily have a weekly seasonality (frequency=7) and an monthly seasonality (frequency=7x30=210)? I need the last 365 days?</p>
  
  <p>Have any way to put the frequency by day of the week and by month? Another thing, does it make any difference I take the whole last year or just a part of it to use in the Holt-Winters method? </p>
  
  <p>Thanks in advance :)</p>