Combining the Rows of All Columns into a Single Column

Question

How do you combine all the rows in all columns into a single column? I would like to append the rows in C2 and C3 to C1. That is, have one column, C1, with 15 rows, each with their respective values.

Please include any code and errors as formatted text not images meta.https://meta.stackoverflow.com/questions/285551/why-not-upload-images-of-code-errors-when-asking-a-question/285557#285557 — Geneva, Mar 04 '22 at 02:32
similar question: https://stackoverflow.com/questions/34376053/pandas-dataframe-stack-multiple-column-values-into-single-column — Geneva, Mar 04 '22 at 02:45

score 0 · Answer 1 · answered Mar 04 '22 at 02:37

One way is to create a new DataFrame from the reshaped numpy array underlying the original DataFrame, using order='F' to stack columns on top of each other:

df_new = pd.DataFrame(df.to_numpy().reshape(-1, 1, order='F'), 
                      columns=['C1'])

Relevant section of the numpy.reshape documentation:

order : {‘C’, ‘F’, ‘A’}, optional

Read the elements of a using this index order, and place the elements into the reshaped array using this index order. ‘C’ means to read / write the elements using C-like index order, with the last axis index changing fastest, back to the first axis index changing slowest. ‘F’ means to read / write the elements using Fortran-like index order, with the first index changing fastest, and the last index changing slowest

score 0 · Answer 2 · answered Mar 04 '22 at 02:50

One way is to use pd.DataFrame.melt:

df.melt()

Output:

   variable value
0        C1     A
1        C1     B
2        C1     C
3        C1     D
4        C1     E
5        C2     F
6        C2     G
7        C2     H
8        C2     I
9        C2     J
10       C3     K
11       C3     L
12       C3     M
13       C3     N
14       C3     O

Combining the Rows of All Columns into a Single Column

2 Answers2