python - Coloring Cells in Pandas

16
votes

I am able to import data from an excel file using 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 DataFrame. I would like to colour some cells in that data based on conditions defined in another function and export the same (with colour coding) to an Excel file.

Can someone tell me how should I go about this?

Thank you.

4
pythonpandasipython
Which library should I be using for it then? - Rahul Wadhwani
xlwt or xlutils. May be also xlwings.org (free) or datanitro.com (paid) for controlling excel directly. Pandas is not designed to manipulate excel files, it just reads from them and makes easy to make calculations. - elyase
openpyxl is well maintained and has seen many recent update - nitin
Are you looking to generate hexadecimal colors based on the values pulled from the spreadsheet, or actually color the cells in the Excel Workbook? Sorry, I wasn't clear on that point from your question. - benjaminmgross
You can use the xlsxwriter engine from Pandas to apply a conditional format to data in an Excel worksheet. See this answer to Easiest way to create a color gradient on excel using python/pandas?. That may be close to what you want to do. - jmcnamara

4 Answers

43
votes

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.

2
votes

There are quite a few ideas about styling the cells on the Pandas website. However it ist mentioned: This is a new feature and still under development. We'll be adding features and possibly making breaking changes in future releases

1
votes

try something like this:

with pandas.io.excel.ExcelWriter(path=Path, engine="xlsxwriter") as writer:
   sheet = writer.book.worksheets()[0]
   sheet.write(x, y, value, format) #format is what determines the color etc.

More info here: https://xlsxwriter.readthedocs.org/format.html

1
votes

The most simple way is to use applymap and lambda if you only want to highlight certain values:

df.style.applymap(lambda x: "background-color: red" if x>0 else "background-color: white")