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from

Operator

from source data from pools, files, or URIs

Synopsis

from <pool>[@<commitish>]
from <pattern>
file <path> [format <format>]
get <uri> [format <format>]
from (
pool <pool>[@<commitish>] [ => <leg> ]
pool <pattern>
file <path> [format <format>] [ => <leg> ]
get <uri> [format <format>] [ => <leg> ]
...
)

Description

The from operator identifies one or more data sources and transmits their data to its output. A data source can be

  • the name of a data pool in a Zed lake, with optional commitish;
  • the names of multiple data pools, expressed as a regular expression or glob pattern;
  • a path to a file; or
  • an HTTP, HTTPS, or S3 URI. Paths and URIs may be followed by an optional format specifier.

Sourcing data from pools is only possible when querying a lake, such as via the zed command or Zed lake API. Sourcing data from files is only possible with the zq command.

When a single pool name is specified without @-referencing a commit or ID, or when using a pool pattern, the tip of the main branch of each pool is accessed.

In the first four forms, a single source is connected to a single output. In the fifth form, multiple sources are accessed in parallel and may be joined, combined, or merged.

A data path can be split with the fork operator as in

from PoolOne | fork (
=> op1 | op2 | ...
=> op1 | op2 | ...
) | merge ts | ...

Or multiple pools can be accessed and, for example, joined:

from (
pool PoolOne => op1 | op2 | ...
pool PoolTwo => op1 | op2 | ...
) | join on key=key | ...

Similarly, data can be routed to different paths with replication using the switch operator:

from ... | switch color (
case "red" => op1 | op2 | ...
case "blue" => op1 | op2 | ...
default => op1 | op2 | ...
) | ...

Input Data

Examples below below assume the existence of the Zed lake created and populated by the following commands:

export ZED_LAKE=example
zed -q init
zed -q create coinflips
echo '{flip:1,result:"heads"} {flip:2,result:"tails"}' | zed -q -use coinflips load -
zed -q -use coinflips branch trial
echo '{flip:3,result:"heads"}' | zed -q -use coinflips@trial load -
zed -q create numbers
echo '{number:1,word:"one"} {number:2,word:"two"} {number:3,word:"three"}' | zed -q -use numbers load -
zed query -f text 'from :branches | yield pool.name + "@" + branch.name | sort'

The lake then contains the two pools:

coinflips@main
coinflips@trial
numbers@main

The following file hello.zson is also used.

{greeting:"hello world!"}

Examples

Source structured data from a local file

zq -z 'file hello.zson | yield greeting'

=>

"hello world!"

Source data from a local file, but in line format

zq -z 'file hello.zson format line'

=>

"{greeting:\"hello world!\"}"

Source structured data from a URI

zq -z 'get https://raw.githubusercontent.com/brimdata/zui-insiders/main/package.json | yield productName'

=>

"Zui - Insiders"

Source data from the main branch of a pool

zed -lake example query -z 'from coinflips'

=>

{flip:2,result:"tails"}
{flip:1,result:"heads"}

Source data from a specific branch of a pool

zed -lake example query -z 'from coinflips@trial'

=>

{flip:3,result:"heads"}
{flip:2,result:"tails"}
{flip:1,result:"heads"}

Count the number of values in the main branch of all pools

zed -lake example query -f text 'from * | count()'

=>

5

Join the data from multiple pools

zed -lake example query -z '
from (
pool coinflips => sort flip
pool numbers => sort number
) | join on flip=number word'

=>

{flip:1,result:"heads",word:"one"}
{flip:2,result:"tails",word:"two"}