title: Plotly: How can I set marker size based on column value?
body: <p>I am trying to use plotly (version 4.6.0) to create plots, but having trouble with the markers/size attribute.</p>
  <p>I am using the Boston housing price dataset in my example. I want to use the value in one of the columns of my dataframe to set a variable size for the marker, but I get an error when I use a direct reference to the column (<code>size='TAX'</code>). I can set the size to a constant (<code>size=1</code>) without issues.</p>
  <p>I found some examples online, but they generate a <code>ValueError</code> when I try to use them. How can I avoid this error? Code and error are shown below.</p>
  <pre><code>    import chart_studio.plotly as py
      import plotly.graph_objs as go
      from plotly.offline import iplot, init_notebook_mode
      import cufflinks
      cufflinks.go_offline(connected=True)
      init_notebook_mode(connected=True)
      import pandas as pd
      from sklearn.datasets import load_boston
      
      boston = load_boston()
      df = pd.DataFrame(boston.data, columns=boston.feature_names)
      y = boston.target
      df['RAD_CAT']=df['RAD'].astype(str)
      
      df.iplot(
          x='CRIM',
          y='INDUS',
          size='TAX',
          #size=1,
          text='RAD',
          mode='markers',
          layout=dict(
              xaxis=dict(type='log', title='CRIM'),
              yaxis=dict(title='INDUS'),
              title='CRIM vs INDUS Sized by RAD'))
      
      ValueError:  
          Invalid value of type 'builtins.str' received for the 'size' property of scatter.marker  
              Received value: 'TAX'  
      
          The 'size' property is a number and may be specified as:  
            - An int or float in the interval [0, inf]  
            - A tuple, list, or one-dimensional numpy array of the above  
  </code></pre>