Changing the Structure of a Dataframe in Python

Question

I need help to change the structure to a pandas dataframe with many columns like the example:

original dataframe:

| xx | yy | zz | a | b | c | k |
|:---|:---|:---|:--|:--|:--|:--|
| x1 | y1 | z1 | 0 | 2 | 1 | 3 |
| x2 | y2 | z2 | 1 | 0 | 2 | 0 |

I need just the first 3 columns and change the rest

new dataframe:

| xx | yy | zz | valor | nueva columna| 
|:---|:---|:---|:--|:--|
| x1 | y1 | z1 | 0 | a |
| x1 | y1 | z1 | 2 | b |
| x1 | y1 | z1 | 1 | c |
| x1 | y1 | z1 | 3 | k |
| x2 | y2 | z2 | 1 | a |
| x2 | y2 | z2 | 0 | b |
| x2 | y2 | z2 | 2 | c |
| x2 | y2 | z2 | 0 | k |

I get a solution with a for loop, but in colab when the columns and rows are many the time is excessive

Use DataFrame.melt.

Henry Yik
– Henry Yik

2021-10-14 16:27:05 +00:00
Commented Oct 14, 2021 at 16:27 — Henry Yik
– Henry Yik, Commented Oct 14, 2021 at 16:27

EBDS · Accepted Answer · 2021-10-14 16:51:09Z

1

df1 = df.set_index(['xx','yy','zz']).stack()
df1.reset_index()

answered Oct 14, 2021 at 16:51

EBDS

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3 Comments

tlentali Over a year ago

Nice @EBDS, you can even make it shorter by adding the reset_index() at the end of the first line like so : df.set_index(['xx','yy','zz']).stack().reset_index().

TKross Over a year ago

Thank you, it work very fine for me.

EBDS Over a year ago

@TKross kindly click the tick to accept the answer. Thanks.

tlentali · Accepted Answer · 2021-10-14 16:55:07Z

0

As suggested by @HenryYik, melt works and provide the expected result :

>>> pd.melt(df, id_vars=['xx', 'yy', 'zz'], value_vars=['a', 'b', 'c', 'k']).sort_values(by=['xx'])
    xx  yy  zz  variable    value
0   x1  y1  z1  a           0
2   x1  y1  z1  b           2
4   x1  y1  z1  c           1
6   x1  y1  z1  k           3
1   x2  y2  z2  a           1
3   x2  y2  z2  b           0
5   x2  y2  z2  c           2
7   x2  y2  z2  k           0

UPDATE : As suggested by @Nesha25, a sort_values is added to get the exact expected output. Thanks @Nesha25.

edited Oct 14, 2021 at 16:55

answered Oct 14, 2021 at 16:42

tlentali

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1 Comment

TKross Over a year ago

it work how i want.I really need to know all that pandas can offer

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