title: updating a Dash plot with drop-down filters
body: <p>I am looking to have 2 dropdowns (one for dates and another sect_id) to filter and update the plot on my dashboard and I am feeling quite confused about the callback and function to create. Here are my data :</p>
  
  <pre><code>  sect_id   Date    Measure1  Measure2  Measure3  Total %
    L19801  01-01-17    12        65        0       33
    L19801  01-01-17    19        81        7       45
    M18803  01-01-17    15        85        7       45
    M19803  01-01-17    20        83        2       52
    xxxxxx  xxxxxxx     xx        xx        x       xx
    xxxxxx  xxxxxxx     xx        xx        x       xx
  </code></pre>
  
  <p>I am looking to scatter Measure1 against Measure3  and have two dropdowns. here what I have done:</p>
  
  <pre><code>  year_options = []
    for date in df['Date'].unique():
             date_options.append({'label':str(date),'value':date})
  
    app=dash.Dash()
  
  
  app.layout = html.Div([
  dcc.Graph(id='graph'),
  dcc.Dropdown(id='date_picker',options=date_options,value=df['Date'][1])])
  </code></pre>
  
  <p>I am currently trying with only one dropdown (the date) and I am very confused about what I have done the layout, the dropdown and the callback.</p>