Pandas copy column names from one dataframe to another

Question

Let’s say that we have two pandas data frames. The first one hasn’t got column names:

no_col_names_df = pd.DataFrame(np.array([[1,2,3], [4,5,6], [7,8,9]]))

The second has:

col_names_df = pd.DataFrame(np.array([[10,2,3], [4,45,6], [7,18,9]]),
                           columns=['col1', 'col2', 'col3'])

What I want to do is to get copy column names from the col_names_df to no_col_names_df so that the following data frame is created:

    col1    col2    col3
0   1       2       3
1   4       5       6
2   7       8       9

I’ve tried the following:

new_df_with_col_names = pd.DataFrame(data=no_col_names_df, columns=col_names_df.columns)

but instead of values from the no_col_names_df I get NaNs.

Asked By: balkon16

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Source

Answer 1

The simplest way is to directly assign the columns of col_names_df to the ones of no_col_names_df:

no_col_names_df.columns = col_names_df.columns

     col1  col2  col3
0     1     2     3
1     4     5     6
2     7     8     9

Answered By: yatu

Answer 2

If you’re getting nan then most likely the issue is the data parameter, try this:

new_df_with_col_names = pd.DataFrame(data=no_col_names_df.values, columns=col_names_df.columns)

output:

   col1  col2  col3
0     1     2     3
1     4     5     6
2     7     8     9

Answered By: Yuca

Answer 3

Just like you have used columns from the dataframe with column names, you can use values from the dataframe without column names:

new_df_with_col_names = pd.DataFrame(data=no_col_names_df.values, columns=col_names_df.columns)

In [4]: new_df_with_col_names = pd.DataFrame(data=no_col_names_df, columns=col_names_df.columns)

In [5]: new_df_with_col_names
Out[5]:
   col1  col2  col3
0   NaN   NaN   NaN
1   NaN   NaN   NaN
2   NaN   NaN   NaN

In [6]: new_df_with_col_names = pd.DataFrame(data=no_col_names_df.values, columns=col_names_df.columns)

In [7]: new_df_with_col_names
Out[7]:
   col1  col2  col3
0     1     2     3
1     4     5     6
2     7     8     9

Answered By: jo9k

Answer 4

This:

pd.DataFrame(data=no_col_names_df, columns=col_names_df.columns)

gives you all ‘NaN’ dataframe because you pass a dataframe to construct a new dataframe and assign new columns to it. Pandas essentially constructs identical dataframe and does reindex along axis 1on it. In other words, that command is equivalent to doing:

no_col_names_df.reindex(col_names_df.columns, axis=1)

You need either change directly no_col_names_df.columns or passing no_col_names_df.values

Answered By: Andy L.

Answer 5

I have tried the simplest one and it is worked for me;

no_col_names_df.columns = col_names_df.columns

Answered By: cinsdikici

Pandas copy column names from one dataframe to another

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