writing data into multi-index pandas dataframe

Question

I am trying to write data into individual cell of my pandas dataframe but am not able to do it.

For example, my initialized dataframe looks like this:

                                  PF44         PF62        PF12         

                                 aa   ss      aa   ss      aa   ss 
1B38:A|ABCDE|DDFE|QUAD           NaN  NaN     NaN  NaN     NaN  NaN

I can access a particular element of my dataframe using the following command:

>>>feat_df.loc['1B38:A|ABCDE|DDFE|QUAD']['PF44']['ss']

and the output is nan. However, if I want to change this to say a number 5 or a text 'test', I used the following commands:

>>>feat_df.loc['1B38:A|ABCDE|DDFE|QUAD']['PF44']['ss'] =5

or

>>>feat_df.loc['1B38:A|ABCDE|DDFE|QUAD']['PF44']['ss']='test'

neither returned any error but when the check the value:

>>>feat_df.loc['1B38:A|ABCDE|DDFE|QUAD']['PF44']['ss']

its still shows

nan

What does feat_df.index and feat_df.columns return? What does feat_df.head(5).to_dict() Output. Add this to you question so we can get a clear structure of your dataframe. — Scott Boston
– Scott Boston, Commented Jun 5, 2018 at 19:56
It seems like you are modifying the copy of dataframe and not dataframe itself. Does the IDE show any warnings? — harpan
– harpan, Commented Jun 5, 2018 at 20:04

Scott Boston · Accepted Answer · 2018-06-05 20:03:10Z

1

IIUC, try this:

feat_df.loc['1B38:A|ABCDE|DDFE|QUAD', ('PF44','ss')] = 5

or

feat_df.loc['1B38:A|ABCDE|DDFE|QUAD', ('PF44','ss')] = 'test'

Use tuples to access MultiIndex Column headers.

answered Jun 5, 2018 at 20:03

Scott Boston

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