filter

Written as filter(argnum flags):options in a transform expression.

Minimum arguments	1
Maximum arguments	no limit
Default arguments	1
Argument modes	MULTIPLE_ARRAYS, MULTIPLE_DICTS

Documentation

Filter out values failing a check from a list of arguments.

The check is specified as a nested transform, and that transform’s output value determines the input value:

• passes the check, if the transform doesn’t raise any error and output value is truthy, otherwise
• fails the check

These values are considered truthy:

• non-empty text, e.g. ‘hello’
• numbers not equal to zero, e.g. 1, -1, 18
• non-empty array, e.g. [null, 0]
• non-empty dict/map

The nested transform for the check purpose can be omitted, in which case, each value themselves being truthy or not, decides if they are kept or removed.

Features:

• removes all values failing the check from input arguments
• preserves order of remaining values
• works with any number of arguments
• returns a new list containing only values passing the check

Flags

Flag	Letter
spread_input	s
spread_output	S
noncaptive_input	I
arg_num_flexible	f

Examples

Basic filtering

Input args: ["Hello",null,"World",null]
Transforms: "filter(*):"
Output: ["Hello","World"]

Mixed types

Input args: [1,null,"text",null,3.14,false,""]
Transforms: "filter(*):"
Output: [1,"text",3.14]

Empty result

Input args: [null,null,null]
Transforms: "filter(*):"
Output: []

Mixed types and nested transform

Input args: [1,null,"text",null,3.14,false,""]
Transforms: "filter(*):regex:ex"
Output: ["text"]

Explicit nested pipeline to filter args by keeping those with upper cased form equal to “HELLO”

Input args: ["Hello","World"]
Transforms: "filter(*):pipeline(1):[\"cased:upper\", \"HELLO\", \"cmp:=\"]"
Output: ["Hello"]

Implicit nested pipeline to filter args by keeping those with upper cased form equal to “HELLO”

Input args: ["Hello","World"]
Transforms: "filter(*):[\"cased:upper\", \"HELLO\", \"cmp:=\"]"
Output: ["Hello"]