# Some useful melt / pivot stuff for pandas DataFrames
```python
pip install a-pandas-ex-melt-pivot-tools
```
```python
from a_pandas_ex_melt_pivot_tools import pd_add_stack_melt_tools
pd_add_stack_melt_tools()
import pandas as pd
df = pd.DataFrame(
{
"A": ["foo", "foo", "foo", "foo", "foo", "bar", "bar", "bar", "bar"],
"B": ["one", "one", "one", "two", "two", "one", "one", "two", "two"],
"C": [
"small",
"large",
"large",
"small",
"small",
"large",
"small",
"small",
"large",
],
"D": [1, 2, 2, 3, 3, 4, 5, 6, 7],
"E": [2, 4, 5, 5, 6, 6, 8, 9, 9],
}
)
print('___________________________________')
print(f'{df}\n\n')
print('___________________________________')
print(f"{df.ds_pivot_to_list(columns=['A'])}\n\n")
print(f"{df.ds_pivot_to_list(columns=['A','B'])}\n\n")
print(f"{df.ds_pivot_to_list(columns=['A','B', 'C'],stack=True)}\n\n")
print(f"{df.ds_pivot_to_list_no_old_index_column(columns=['A'])}\n\n")
print(f"{df.ds_pivot_to_list_no_old_index_column(columns=['A','B'])}\n\n")
print(f"{df.ds_pivot_to_list_no_old_index_column(columns=['A','B', 'C'],stack=True)}\n\n")
print(f"{df.ds_pivot_to_list_no_old_index_column_transposed(columns=['A'],stack=True)}\n\n")
print(f"{df.ds_pivot_to_list_no_old_index_column_transposed(columns=['A','B'],stack=True)}\n\n")
print(f"{df.ds_pivot_to_list_no_old_index_column_transposed(columns=['A','B', 'C'],stack=True)}\n\n")
___________________________________
A B C D E
0 foo one small 1 2
1 foo one large 2 4
2 foo one large 2 5
3 foo two small 3 5
4 foo two small 3 6
5 bar one large 4 6
6 bar one small 5 8
7 bar two small 6 9
8 bar two large 7 9
___________________________________
bar ... old_columns
old_columns ...
B [one, one, two, two, None] ... [B, B, B, B, B]
C [large, small, small, large, None] ... [C, C, C, C, C]
D [4, 5, 6, 7, None] ... [D, D, D, D, D]
E [6, 8, 9, 9, None] ... [E, E, E, E, E]
[4 rows x 3 columns]
bar ... old_columns
one ...
old_columns ...
C [large, small, None] ... [C, C, C]
D [4, 5, None] ... [D, D, D]
E [6, 8, None] ... [E, E, E]
[3 rows x 5 columns]
bar foo old_columns
one two one two
old_columns
D NaN NaN NaN NaN [D, D]
large [4, None] [7, None] [2, 2] NaN NaN
small [5, None] [6, None] [1, None] [3, 3] NaN
E NaN NaN NaN NaN [E, E]
large [6, None] [9, None] [4, 5] NaN NaN
small [8, None] [9, None] [2, None] [5, 6] NaN
bar foo
B [one, one, two, two] [one, one, one, two, two]
C [large, small, small, large] [small, large, large, small, small]
D [4, 5, 6, 7] [1, 2, 2, 3, 3]
E [6, 8, 9, 9] [2, 4, 5, 5, 6]
bar foo
one two one two
C [large, small] [small, large] [small, large, large] [small, small]
D [4, 5] [6, 7] [1, 2, 2] [3, 3]
E [6, 8] [9, 9] [2, 4, 5] [5, 6]
bar foo
one two one two
D large [4] [7] [2, 2] NaN
small [5] [6] [1] [3, 3]
E large [6] [9] [4, 5] NaN
small [8] [9] [2] [5, 6]
bar B one
C large
D 4
E 6
B one
...
foo E 5
B two
C small
D 3
E 6
Length: 3524, dtype: object
bar one C large
D 4
E 6
C large
D 4
...
foo two D 3
E 5
C small
D 3
E 6
Length: 153, dtype: object
bar one large D 4
E 6
small D 5
E 8
two large D 7
E 9
small D 6
E 9
foo one large D 2
E 4
D 2
E 5
D 2
E 4
D 2
E 5
small D 1
E 2
two small D 3
E 5
D 3
E 6
D 3
E 5
D 3
E 6
dtype: object
```
