DOC: Pivot() example call incorrectly used and would give "error: duplicate index"

[mheskett]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

doc/source/user_guide/reshaping.rst

Documentation problem

the table given as an example for pivot() is wrong and cant be used. it would return "error duplicate index" as there are duplicate values in the column given for "index" parameter.

Suggested fix for documentation

The "foo" column must contain unique values

[goutam-kul]

@mheskett It will not throw ValueError: Index contains duplicate entries, cannot reshape , because the index (fool) and columns (bar) have unique combinations:

import pandas as pd

data = {"foo": ['one', 'one', 'one', 'two', 'two', 'two'],
    "bar": ['A', 'B', 'C', 'A', 'B', 'C'],
    "baz": [1, 2, 3, 4, 5, 6],
    "zoo": ['x', 'y', 'z', 'q', 'w', 't']
}

df = pd.DataFrame(data=data)
# print(df)
out = df.pivot(index='foo', columns='bar', values='baz')
print(out)

Output:

bar  A  B  C
foo         
one  1  2  3
two  4  5  6

---

What happens if I introduce a non-unique combination? yes it will throw duplicate index error. E.g:

data = {"foo": ['one', 'one', 'one', 'two', 'two', 'two'],
    "bar": ['A', 'A', 'C', 'A', 'B', 'C'],
    "baz": [1, 2, 3, 4, 5, 6],
    "zoo": ['x', 'y', 'z', 'q', 'w', 't']
}

Output:

ValueError: Index contains duplicate entries, cannot reshape

---

While you can use pivot_table method when your have duplicate values in index and column

out = df.pivot_table(index='foo', columns='bar', values='baz')
print(out)

Output:

bar    A    B    C
foo               
one  1.5  NaN  3.0
two  4.0  5.0  6.0

Hope this helps!

[mheskett]

thank you. so in that case, the ValueError message is misleading. I can raise a separate issue about that. it should read "must contain unique combinations of index and column"

[rhshadrach]

I can raise a separate issue about that.

We can rework this issue instead. Why do you feel the ValueError is misleading?