First / List Layer
Extract the first element from each variable-length list. Similar to list[0] indexing in Python or head(1) in R. Returns a column containing the first element of each list.
Example transformation:
| lists | first |
|---|---|
| [1, 2, 3, 4] | 1 |
| [apple, banana] | apple |
| [true] | true |
| [null, 2, 3] | null |
| [] | null |
Common applications:
- Getting most recent events in time-ordered lists
- Extracting primary categories from tag lists
- Finding initial states in sequences
- Accessing first readings in measurement series
- Getting top priorities from ranked items
- Extracting lead elements from variable sequences
Note: Lists can have any length, including empty. Returns null for empty lists or if first element is null. Preserves original element type. Particularly useful for accessing initial elements in varying-length sequences.
Table
0
0
Table
Select
columnThe variable-length list column to access. Supports various types:
- Numeric lists: [1, 2, 3], [4, 5]
- String lists: [first, second, third], [single]
- Boolean lists: [true, false], [true]
- Date/time lists: [2024-01-01, 2024-01-02], [] Lists can have different lengths, including empty lists
AsColumn
nameName 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.