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Coloring Cells in Pandas

I am able to import data from an Excel file with Pandas by using:

xl = read_excel('path_to_file.xls', 'Sheet1', index_col=None, na_values=['NA'])

Now that I have all the data in xl as a DataFrame, I would like to colour some cells in that data based on conditions defined in another function before exporting the same data (with colour coding) to an Excel file.

How can I color specific cells in a Pandas DataFrame?

Solution

  • Pandas has a relatively new Styler feature where you can apply conditional formatting type manipulations to dataframes. http://pandas.pydata.org/pandas-docs/stable/style.html

    You can use some of their built-in functions like background_gradient or bar to replicate excel-like features like conditional formatting and data bars. You can also format cells to display percentages, floats, ints, etc. without changing the original dataframe.

    Here's an example of the type of chart you can make using Styler (this is a nonsense chart but just meant to demonstrate features):

    enter image description here

    To harness the full functionality of Styler you should get comfortable with the Styler.apply() and Styler.applymap() APIs. These allow you to create custom functions and apply them to the table's columns, rows or elements. For example, if I wanted to color a +ive cell green and a -ive cell red, I'd create a function 

    def _color_red_or_green(val):
    color = 'red' if val < 0 else 'green'
    return 'color: %s' % color

    and call it on my Styler object, i.e., df.style.applymap(_color_red_or_green).

    With respect to exporting back to Excel, as far as I'm aware this is not supported in Styler yet so I'd probably go the xlsxwriter route if you NEED Excel for some reason. However, in my experience this is a great pure Python alternative, for example along with matplotlib charts and in emails/reports.