parquet-cli reports nested columns as null
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Assessment
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Newbie friendliness
- 35/100
Research direction
Reproduce the issue with Parquet CLI 1.15.0 using parquet schema, parquet dictionary -c subjects.list.element, and cat or head on catalog.parquet. Compare the nested-column values reported by the dictionary command with the displayed records and inspect the parquet-cli path handling those commands. Done means cat and head show nested arrays instead of incorrectly displaying them as null.
Written by the indexing model from the issue text.
Description
Describe the bug, including details regarding any error messages, version, and platform.
Using Parquet CLI 1.15.0 via Mac Homebrew, I noticed some surprising behaviour with the parquet-cli and nested columns.
parquet schema catalog.parquet returns a schema showing the nested types (I've trimmed the field list slightly):
{
"type" : "record",
"name" : "schema",
"fields" : [ {
"name" : "item_id",
"type" : "string"
}, {
"name" : "title",
"type" : [ "null", "string" ],
"default" : null
}, {
"name" : "language",
"type" : [ "null", "string" ],
"default" : null
}, {
"name" : "subjects",
"type" : [ "null", {
"type" : "array",
"items" : {
"type" : "record",
"name" : "list",
"fields" : [ {
"name" : "element",
"type" : "string"
} ]
}
} ],
"default" : null
}, {
"name" : "authors",
"type" : [ "null", {
"type" : "array",
"items" : {
"type" : "record",
"name" : "list",
"namespace" : "list2",
"fields" : [ {
"name" : "element",
"type" : "string"
} ]
}
} ],
"default" : null
} ]
}
parquet dictionary -c subjects.list.element catalog.parquet will return the expected values for those fields as well:
Row group 0 dictionary for "subjects.list.element":
0: "Bestsellers"
1: "Biography"
2: "Fantasy Fiction"
3: "Music Theory"
4: "Disability"
5: "Family"
6: "Young Adult"
However, when using cat or head to display the file contents those fields are displayed as null:
{"bmc_id": "id1", "title": null, "language": "en", "subjects": null, "authors": null}
{"bmc_id": "id2", "title": null, "language": "en", "subjects": null, "authors": null,}
{"bmc_id": "id3", "title": null, "language": "en", "subjects": null, "authors": null}
Other tools like PyArrow or Pandas do display those values as arrays. I created this as a bug because it looks like it's working and if those fields are nullable, there's no way to tell whether the null value is correct.
Component(s)
No response
- Dominant language
- Java
- Stars
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- Forks
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- Avg merge
- 6d 16h
- Merged PRs (30d)
- 36
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