snowflakedb / snowflakedb/snowpark-python

SNOW-704114: Implement `DataFrame.summary` to show percentiles

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feature
Dominant language
Python
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341
Forks
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Avg merge
4d 16h
Merged PRs (30d)
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Description

Update: As of Mar.27 2023, @sfc-gh-stan and @sfc-gh-gfrere discussed this and concluded we should implement DataFrame.summary() to display the percentiles instead of modifying the existing DataFrame.describe().

What is the current behavior?

    Example::
        >>> df = session.create_dataframe([[1, 2], [3, 4]], schema=["a", "b"])
        >>> desc_result = df.describe().sort("SUMMARY").show()
        -------------------------------------------------------
        |"SUMMARY"  |"A"                 |"B"                 |
        -------------------------------------------------------
        |count      |2.0                 |2.0                 |
        |max        |3.0                 |4.0                 |
        |mean       |2.0                 |3.0                 |
        |min        |1.0                 |2.0                 |
        |stddev     |1.4142135623730951  |1.4142135623730951  |
        -------------------------------------------------------

Percentiles are not shown.

What is the desired behavior?

Show percentiles 25, 50, 75 like Pandas.describe(). Using updated approximate percentile
'alter session set APPROX_PERCENTILE_EXACT_IF_POSSIBLE = true;’

How would this improve snowflake-snowpark-python?

It would match Pandas behavior and is requested by customers. Given the improvements being made to APPROX_PERCENTILE% we should implement this change. Before we may have thought this was too expensive or inaccurate due to APPROX_PERCENTILE% issues on few samples.

References, Other Background

APPROX_PERCENTILE is being updated by the SQL Compiler team to allow for a larger buffer usage and if the buffer doesn't fill PERCENTILE_CONT is automatically used.
https://snowflakecomputing.atlassian.net/browse/SNOW-704037

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by locating the DataFrame.summary() and existing DataFrame.describe() entry points in the snowpark-python codebase, then inspect how summary statistics are assembled. Verify the expected percentile behavior against the provided example and Pandas.describe(), including the requested approximate-percentile session setting. Done means DataFrame.summary() displays the 25th, 50th, and 75th percentiles without changing DataFrame.describe().

Written by the indexing model from the issue text.

Assessment

Tech stack
python, sql
Domain
data
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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