title: How to properly create a HeatMap with Bokeh
body: <p>I'm trying to replicate the HeatMap shown in <a href="https://stackoverflow.com/questions/14391959/heatmap-in-matplotlib-with-pcolor">this question</a> using Bokeh instead of matplotlib. I can't get it quite right though. The existing examples have not helped me to understand what I'm doing wrong. My humble attempt</p>
  
  <pre><code>from bokeh.io import output_notebook; output_notebook()
  from bokeh.charts import HeatMap, show
  from bokeh.palettes import RdYlGn6
  import pandas as pd
  import numpy as np
  
  nba = pd.read_csv(urlopen("http://datasets.flowingdata.com/ppg2008.csv"), index_col=0)
  
  # Normalize the data columns and sort.
  nba = (nba - nba.mean()) / (nba.max() - nba.min())
  nba.sort('PTS', inplace=True)
  
  score = []
  for x in nba.apply(tuple):
    score.extend(x)
  
  data = {
    'players': list(nba.index) * len(nba.columns),
    'metric':  list(nba.columns) * len(nba.index),
    'score':   score,
  }
  
  hm = HeatMap(data, x='metric', y='players',values='score', title='Fruits', stat=None)
  show(hm)
  </code></pre>
  
  <p>Gives</p>
  
  <p><a href="https://i.stack.imgur.com/CY1pr.png" rel="noreferrer"><img src="https://i.stack.imgur.com/CY1pr.png" alt="enter image description here"></a></p>
  
  <p>Note that, despite the similar title, <a href="https://stackoverflow.com/questions/35189203/bokeh-heatmap-usage">this</a> does not answer my question. It's not the same error and I'm using Bokeh 0.12.3</p>