Get / List Layer

Extract element at specified index from each variable-length list. Similar to list[i] indexing in Python or nth() in R. Returns a column containing elements at the specified position, supporting both positive and negative indexing.

Example transformation:

Positive indexing (index=1):

lists	element
[1, 2, 3, 4]	2
[x, y]	y
[a]	null
[]	null
[null, b, c]	b

Negative indexing (index=-1):

lists	element
[1, 2, 3, 4]	4
[x, y]	y
[a]	a
[]	null
[a, b, null]	null

Common applications:

Accessing most recent entries in time-ordered lists
Extracting specific elements from log sequences
Getting last transaction from history
Selecting specific measurements from samples
Accessing elements by relative position
Processing periodic data points

Note: Lists can have any length. Returns null for out-of-bounds indices. Positive indices start from 0, negative indices count from end (-1 for last element). Preserves null values at specified position. Particularly useful for accessing elements in variable-length sequences by relative position.

Table

Select

column

The variable-length list column to access. Supports various types:

Numeric lists: [1, 2, 3, 4], [5, 6]
String lists: [first, second, third], [a]
Boolean lists: [true, false, true], [false]
Date/time lists: [2024-01-01, 2024-01-02], [] Lists can have different lengths, including empty lists

Index

oneof

Fixed

i32

Position to extract (Index). Supports both directions: Positive (from start, 0-based):

0: First element
1: Second element
2: Third element Negative (from end):
-1: Last element
-2: Second-to-last element
-3: Third-to-last element

SelectIdx

column

Column containing indices. Each row can specify a different position to extract. Supports both positive and negative indices. Must contain valid integer values.

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.