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MINOR: [Docs] Clarify struct validity masking with 'hidden data' example #49554

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raulcd merged 1 commit into from
Mar 20, 2026
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MINOR: [Docs] Clarify struct validity masking with 'hidden data' example #49554

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7 changes: 7 additions & 0 deletions docs/source/format/Intro.rst
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Expand Up @@ -296,6 +296,13 @@ key is the field name and the child array its values. The field (key) is
saved in the schema and the values of a specific field (key) are saved in
the child array.

Since child arrays are independent, Arrow does not enforce physical
consistency between the struct's validity bitmap and those of it's children.
Logically, a struct row is only valid if both the parent and the child
bitmaps have a value of 1 for that slot (a logical AND operation).
This allows for "hidden" data to exist in child arrays at null struct
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@raulcd raulcd Mar 19, 2026

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I would personally remove the term hidden as it might give connotations of obfuscation/security related and this is not the intention, the intention is more about avoiding copy and reusing existing buffers. The data is just left in place because it's cheaper:

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This allows for "hidden" data to exist in child arrays at null struct
This allows for data to exist in child arrays at null struct

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@raulcd raulcd Mar 19, 2026

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oh! I've just seen that the term "hidden" appears on the spec. Welp if the spec says so ... I'll leave it to you to decide :)

positions (see ``alice`` below).

.. figure:: ./images/struct-diagram.svg
:alt: Diagram is showing the difference between the struct data type
presented in a Table and the data actually stored in computer
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