title: Plotly: How to use dropdowns with pandas dataframes?
body: <p>I'm writing a small script to plot material data using plotly, I tried to use a dropdown to select which column of my dataframe to display. I can do this by defining the columns one by one but the dataframe will change in size so I wanted to make it flexible.</p>
  
  <p>I've tried a few things and got to this; </p>
  
  <pre><code>for i in df.columns:
      fig = go.Figure()
      fig.add_trace(go.Scatter(x=df.index, y=df[i]))
  
      fig.update_layout(
          updatemenus=[
              go.layout.Updatemenu(
                  buttons=list([
                      dict(
                          args=["values", i],
                          label=i,
                          method="update"
                      ),
                  ]),
                  direction="down",
                  pad={"r": 10, "t": 10},
                  showactive=True,
                  x=0.1,
                  xanchor="left",
                  y=1.1,
                  yanchor="top"
              ),
          ]
      )
      fig.update_layout(
          annotations=[
              go.layout.Annotation(text="Material:", showarrow=False,
                               x=0, y=1.085, yref="paper", align="left")
          ]
      )
  
  fig.show()
  </code></pre>
  
  <p>The chart shows the final column of the df, while dropdown only holds the last column header?</p>
  
  <p>My data looks something like this, where i is the index, the chart and dropdown show column 'G';</p>
  
  <pre><code>i  A  B  C  D  E  F  G
  1  8  2  4  5  4  9  7
  2  5  3  7  7  6  7  3
  3  7  4  9  3  7  4  6
  4  3  9  3  6  3  3  4
  5  1  7  6  9  9  1  9
  </code></pre>