pandas: HTML output with conditional formatting


Question

I am trying to format a table, such that data in each column are formatted in a style depending on their values (similar to conditional formatting in spreadsheet programs). How can I achieve that in pandas using the HTML formatter?

A typical use case is highlighting significant values in a table. For example:

    correlation  p-value
0   0.5          0.1
1   0.1          0.8
2   0.9          *0.01*

pandas allows to define custom formatters for HTML output - to obtain above output one could use:

import pandas as pd
from pandas.core import format
from StringIO import StringIO
buf = StringIO()
df = pd.DataFrame({'correlation':[0.5, 0.1,0.9], 'p_value':[0.1,0.8,0.01]})
fmt = format.DataFrameFormatter(df, 
          formatters={'p_value':lambda x: "*%f*" % x if x<0.05 else str(x)})
format.HTMLFormatter(fmt).write_result(buf)

However, I would like to change the style for significant values (for example, by using bold font).

A possible solution would be to attach a CSS class to <td> tags in the HTML output, which could be then formatted using CSS stylesheet. The above would then become:

<table border="1" class="dataframe">
  <thead>
    <tr style="text-align: right;">
      <th></th>
      <th>correlation</th>
      <th>p_value</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>0</td>
      <td> 0.5</td>
      <td> 0.10</td>
    </tr>
    <tr>
      <td>1</td>
      <td> 0.1</td>
      <td> 0.80</td>
    </tr>
    <tr>
      <td>2</td>
      <td> 0.9</td>
      <td class='significant'> 0.01</td>
    </tr>
  </tbody>
</table>

Edit: As suggested by @Andy-Hayden I can add formatting by simply replacing stars with <span class="signifcant">...</span> in my example:

import pandas as pd
from StringIO import StringIO
buf = StringIO()
significant = lambda x: '<span class="significant">%f</span>' % x if x<0.05 else str(x)
df = pd.DataFrame({'correlation':[0.5, 0.1,0.9], 'p_value':[0.1,0.8,0.01]})
df.to_html(buf, formatters={'p_value': significant})

Newer versions of pandas escape the tags. To avoid it replace last line with:

df.to_html(buf, formatters={'p_value': significant}, escape=False)
1
24
12/6/2013 1:17:59 PM

Accepted Answer

You can use the DataFrame to_html method, which comes with formatters argument.

An easier solution would be to surround by <span class="significant"> and </span>, (rather than *). Note: by default this will be escaped (i.e. < becomes &lt;) so you will need to use the escape=False argument.

22
6/9/2017 6:17:21 PM

Since pandas 0.17.1, it is easy to apply custom formatting to the data frame HTML representation using the styling api.

import pandas as pd

df = pd.DataFrame({
    'correlation':[0.5, 0.1,0.9],
    'p_value':[0.1,0.8,0.01]})
styled_df = df.style.apply(
    lambda x: ['font-weight: bold; background-color: yellow'
               if value <= 0.01 else '' for value in x])
styled_df

enter image description here

The output is rendered automatically in interfaces such as the Jupyter Notebook and the string representation of the HTML can be returned with the render() method.

print(styled_df.render())
<style  type="text/css" >
    #T_4e49b9da_8451_11e8_9166_605718a99a7frow2_col1 {
            font-weight:  bold;
             background-color:  yellow;
            font-weight:  bold;
             background-color:  yellow;
        }</style>  
<table id="T_4e49b9da_8451_11e8_9166_605718a99a7f" > 
<thead>    <tr> 
        <th class="blank level0" ></th> 
        <th class="col_heading level0 col0" >correlation</th> 
        <th class="col_heading level0 col1" >p_value</th> 
    </tr></thead> 
<tbody>    <tr> 
        <th id="T_4e49b9da_8451_11e8_9166_605718a99a7flevel0_row0" class="row_heading level0 row0" >0</th> 
        <td id="T_4e49b9da_8451_11e8_9166_605718a99a7frow0_col0" class="data row0 col0" >0.5</td> 
        <td id="T_4e49b9da_8451_11e8_9166_605718a99a7frow0_col1" class="data row0 col1" >0.1</td> 
    </tr>    <tr> 
        <th id="T_4e49b9da_8451_11e8_9166_605718a99a7flevel0_row1" class="row_heading level0 row1" >1</th> 
        <td id="T_4e49b9da_8451_11e8_9166_605718a99a7frow1_col0" class="data row1 col0" >0.1</td> 
        <td id="T_4e49b9da_8451_11e8_9166_605718a99a7frow1_col1" class="data row1 col1" >0.8</td> 
    </tr>    <tr> 
        <th id="T_4e49b9da_8451_11e8_9166_605718a99a7flevel0_row2" class="row_heading level0 row2" >2</th> 
        <td id="T_4e49b9da_8451_11e8_9166_605718a99a7frow2_col0" class="data row2 col0" >0.9</td> 
        <td id="T_4e49b9da_8451_11e8_9166_605718a99a7frow2_col1" class="data row2 col1" >0.01</td> 
    </tr></tbody> 
</table>

Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow
Icon