How to add a Column named Key into a dictionary of multiple dataframes

Question

Given a dictionary with multiple dataframes in it. How I can add a column to each dataframe with all the rows in that df filled with the key name'?

I tried this code:

for key, df in sheet_to_df_map.items():
    df['sheet_name'] = key

This code does add the key column in each dataframe inside the dictionary, but also creates an additional dataframe.

Can't this be done without creating an additional dataframe?

Furthermore, I want to separate dataframes from the dictionary by number of columns. All the dataframes that have 10 columns concatenated, the ones with 9 concatenated and so on. I don't know how to do this.

Don't see why an extra `df` is being created. It shouldn't be done with the code you provided. — not_speshal, Sep 09 '21 at 20:03
what do you mean by "but also creates an additional dataframe"? — Ben.T, Sep 09 '21 at 20:04
I edited the question so you can see how my code creates a dataframe, from the first key in the dictionary. — Steven González, Sep 09 '21 at 20:33

Fernando Caletti · Answer 1 · 2021-09-09T21:59:51.567

I could do it with the method assign() in the DataFrames and then replacing the hole value in the dictionary, but I don't know in fact if it's this that you want...

 for key, df in myDictDf.items():    
   myDictDf[key] = df.assign(sheet_name=[key for w in range(len(df.index))])

To sort your dictionary, I think you can use an OrderedDict with the columns property of the DataFrames. By using len(df.columns) you can get the quantity of columns for each frame.

I think these links can be useful for you:

https://note.nkmk.me/en/python-pandas-len-shape-size/

https://www.geeksforgeeks.org/python-sort-python-dictionaries-by-key-or-value/

I've found a related question too: Adding new column to existing DataFrame in Python pandas

How to add a Column named Key into a dictionary of multiple dataframes

1 Answers1