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separator parameter in pivot() has no effect #15775

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2 tasks done
jsarbach opened this issue Apr 19, 2024 · 5 comments · Fixed by #15957
Closed
2 tasks done

separator parameter in pivot() has no effect #15775

jsarbach opened this issue Apr 19, 2024 · 5 comments · Fixed by #15957
Labels
documentation Improvements or additions to documentation python Related to Python Polars

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@jsarbach
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Checks

  • I have checked that this issue has not already been reported.
  • I have confirmed this bug exists on the latest version of Polars.

Reproducible example

pl.DataFrame({'ix': [0, 1], 'col1': ['a', 'b'], 'col2': [1, 2], 'val': [1, 2]}).pivot(index='ix', columns=['col1', 'col2'], values='val')
pl.DataFrame({'ix': [0, 1], 'col1': ['a', 'b'], 'col2': [1, 2], 'val': [1, 2]}).pivot(index='ix', columns=['col1', 'col2'], values='val', separator='_')
pl.DataFrame({'ix': [0, 1], 'col1': ['a', 'b'], 'col2': [1, 2], 'val': [1, 2]}).pivot(index='ix', columns=['col1', 'col2'], values='val', separator='letsseparate')

Log output

shape: (2, 3)
┌─────┬─────────┬─────────┐
│ ix  ┆ {"a",1} ┆ {"b",2} │
│ --- ┆ ---     ┆ ---     │
│ i64 ┆ i64     ┆ i64     │
╞═════╪═════════╪═════════╡
│ 0   ┆ 1       ┆ null    │
│ 1   ┆ null    ┆ 2       │
└─────┴─────────┴─────────┘

Issue description

According to the documentation, separator is used as separator/delimiter in generated column names. However, it seems to be ignored (incl. the default _).

Expected behavior

>>> pl.DataFrame({'ix': [0, 1], 'col1': ['a', 'b'], 'col2': [1, 2], 'val': [1, 2]}).pivot(index='ix', columns=['col1', 'col2'], values='val')
shape: (2, 3)
┌─────┬─────────┬─────────┐
│ ix  ┆ a_1     ┆ b_2     │
│ --- ┆ ---     ┆ ---     │
│ i64 ┆ i64     ┆ i64     │
╞═════╪═════════╪═════════╡
│ 0   ┆ 1       ┆ null    │
│ 1   ┆ null    ┆ 2       │
└─────┴─────────┴─────────┘

Installed versions

--------Version info---------
Polars:               0.20.21
Index type:           UInt32
Platform:             Linux-6.5.0-27-generic-x86_64-with-glibc2.38
Python:               3.10.6 (main, Oct  7 2022, 20:19:58) [GCC 11.2.0]
----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          2.2.0
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            0.10.3
fsspec:               2022.8.2
gevent:               <not installed>
hvplot:               <not installed>
matplotlib:           <not installed>
nest_asyncio:         <not installed>
numpy:                1.23.4
openpyxl:             3.0.10
pandas:               2.0.3
pyarrow:              15.0.0
pydantic:             1.10.2
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           <not installed>
xlsx2csv:             0.8.2
xlsxwriter:           <not installed>
@jsarbach jsarbach added bug Something isn't working needs triage Awaiting prioritization by a maintainer python Related to Python Polars labels Apr 19, 2024
@MarcoGorelli MarcoGorelli added documentation Improvements or additions to documentation and removed bug Something isn't working needs triage Awaiting prioritization by a maintainer labels Apr 20, 2024
@MarcoGorelli
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hey - the separator is used if there are multiple values

@jsarbach
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Ah I see, thanks for clarifying.

@reswqa
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reswqa commented Apr 22, 2024

@jsarbach fancy updating the document about this?

@cmdlineluser
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Are there any plans to allow expressions?

i.e.

df.pivot(
    index="ix"
    columns=pl.format("{}_{}", "col1", "col2"),
    values="val"
)

In order to:

(df.with_columns(columns=pl.format("{}_{}", "col1", "col2"))
   .pivot(index="ix", columns="columns", values="val")
)

# shape: (2, 3)
# ┌─────┬──────┬──────┐
# │ ix  ┆ a_1  ┆ b_2  │
# │ --- ┆ ---  ┆ ---  │
# │ i64 ┆ i64  ┆ i64  │
# ╞═════╪══════╪══════╡
# │ 0   ┆ 1    ┆ null │
# │ 1   ┆ null ┆ 2    │
# └─────┴──────┴──────┘

@jsarbach
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@jsarbach fancy updating the document about this?

Ok :-)

This was referenced Apr 27, 2024
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@reswqa @jsarbach @MarcoGorelli @cmdlineluser