Join / List Layer

Combine elements from variable-length string lists into a single string using a specified separator. Similar to Python's str.join() or R's paste(collapse=). Creates a string column where each row contains concatenated list elements.

Example transformation:

With separator=', ':

lists	joined
[red, blue, green, yellow]	red, blue, green, yellow
[x, y]	x, y
[tag1]	tag1
[a, null, c, null]	a, c
[]	null
[null, null]	null

Common applications:

Creating CSV strings from variable-length data
Formatting dynamic tag lists
Building composite descriptions
Concatenating transaction histories
Converting hierarchical paths to strings
Combining multi-value attributes
Formatting search keywords

Note: Only works with string lists. Lists can have any length, including empty. Empty lists produce null output. Supports customizable separators and null handling. Particularly useful for creating delimited text from dynamic data structures.

Table

Select

column

The variable-length string list column to join. Examples:

Tags: [urgent, high-priority, critical]
Path components: [usr, local, bin]
Keywords: [python, data-science]
Categories: [electronics, computers] Lists can have different lengths. Only string elements supported.

Separator

oneof

Fixed

string

String to insert between list elements. Common separators:

', ' for human-readable lists
',' for CSV data
'/' for file paths
'.' for domain names
'-' for compound identifiers
'|' for pipe-separated values

SelectSep

column

Column containing separators. Each row can use a different separator for flexible string formatting. Must contain valid string separators.

IgnoreNulls

bool

true

Control null value handling:

true (default): Skip null values in concatenation: [a, null, c] → 'a, c' [x, y, null] → 'x, y'
false: Return null if list contains any nulls: [a, null, c] → null [x, y, z] → 'x, y, z'

AsColumn

name

Name for the new column. If not provided, the system generates a unique name. If AsColumn matches an existing column, the existing column is replaced. The name should follow valid column naming conventions.