Function lag_str

Source

pub fn lag_str<T: Integer>(
    arr: StringAVT<'_, T>,
    n: usize,
) -> Result<StringArray<T>, KernelError>

Expand description

Accesses string values from previous positions with UTF-8 string handling.

Implements SQL LAG() function for string data, retrieving textual values from earlier positions in the array sequence. Essential for textual analysis, sequential string processing, and comparative text analytics.

§Parameters

arr - String array view containing sequential textual data
n - Lag offset specifying backward position distance

§Returns

Returns Result<StringArray<T>, KernelError> containing:

Success: String values from n positions earlier
Error: KernelError if string processing fails
Empty strings for positions with insufficient history
Null mask indicating lag validity and source availability

§String Lag Semantics

UTF-8 preservation: Maintains proper UTF-8 encoding throughout operation
Null propagation: Null strings in source positions result in null outputs
Memory management: Efficient string copying and allocation strategies
Boundary handling: Positions without history receive empty string defaults

§Applications

Text analysis: Comparing current text with previous entries
Sequential processing: Analysing patterns in ordered textual data
Log analysis: Accessing previous log entries for context
Natural language processing: Context-aware text processing with history

§Examples

use minarrow::StringArray;
use simd_kernels::kernels::window::lag_str;

let arr = StringArray::<u32>::from_slice(&["first", "second", "third"]);
let result = lag_str((&arr, 0, arr.len()), 1).unwrap();
// Output: ["", "first", "second"] - strings lagged by 1 position

lag_str