Head / List Layer

Create a new list containing the first N elements from each variable-length list. Similar to Python's list[:n] or R's head(). If the input list is shorter than N, returns all available elements.

Example transformation:

With N=2:

lists	head
[1, 2, 3, 4]	[1, 2]
[a, b]	[a, b]
[x]	[x]
[]	[]

Common applications:

Creating preview snippets
Limiting sequence lengths
Sampling initial elements
Extracting recent events
Truncating long lists
Creating fixed-length prefixes

Note: Returns fewer elements if input list length < N. Empty lists remain empty. Preserves null values within the taken range.

Table

Select

column

The variable-length list column to truncate. Examples:

Time series: [v1, v2, v3, v4, v5]
Log entries: [log1, log2, log3]
Tag sequences: [tag1, tag2] Lists can have different lengths

N

u32

Number of elements (N) to keep from start of each list. Examples:

1: Keep first element only
2: Keep first two elements
5: Keep first five elements Must be greater than 0

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.