from LearningZq
examples use zq version 1.16.0 and jq version 1.7
The pipe character appears quite frequently in both jq and zq. Here's an example of an
equivalent query in both:
jq -c '[.docs[]
| {title, author_name: .author_name[0], publish_year: .publish_year[0]}
| select(.author_name!=null and .publish_year!=null)
]
| group_by(.author_name)
| [.[] | {author_name: .[0].author_name, count: . | length}]
| sort_by(.count) | reverse | limit(3;.[])' openlibrary.json
zq -j 'over docs
| {title, author_name: author_name[0], publish_year: publish_year[0]}
| has(author_name) and has(publish_year)
| count() by author_name | sort -r count | head 3' openlibrary.json
(Examples taken from this Brim Data article comparing zq and jq).
In jq every program is a series of filters separated by the pipe operator. There are a few places the pipe operator cannot be used, but it's fairly ubiquitous.
zq has a more elaborate and structured syntax. At its highest level, one or more dataflow operators are joined together in a sequence with the pipe character (sequence overview). operator | operator | ...
But within operators, syntax varies and the pipe character isn't used. Field references and expressions are common, and most functions receive arguments passed in parentheses. Function outputs can only be passed to other functions as nested calls, not via the pipe character.
In this example, the who value is replaced with “me” whenever it's “chrismo”:
> zq -j '[{who:"bob"}, {who:"chrismo"}]
| over this
| put who:=replace(who, "chrismo", "me")'
{"who":"bob"}
{"who":"me"}
put is an operation that sets a field to an expression. replace is a function taking three string arguments.
If not all records have a who field, we can use the coalesce function to return an empty string if who is missing, but we cannot use the pipe character like we could in jq between two functions:
❯ zq -j '[{}, {who:"bob"}, {who:"chrismo"}]
| over this
| put who:=((coalesce(who, "") | replace(who, "chrismo", "me"))'
zq: error parsing Zed at line 3, column 39:
| put who:=((coalesce(who, "") | replace(who, "chrismo", "me"))
=== ^ ===
The syntax for put is [put] <field>:=<expr>
and the pipe character is not valid in an expression**. This can be accomplished by nesting the function calls:
❯ zq -j '[{}, {who:"bob"}, {who:"chrismo"}]
| over this
| put who:=replace(coalesce(who, ""), "chrismo", "me")'
{"who":""}
{"who":"bob"}
{"who":"me"}
**well ... there is an exception to this, but that's covered in ZqLateralSubquery.
Prev: ZqImpliedOperatorsCanTrickYou | Up: LearningZq | Next: ZqFunctionsNeedParens
