StringRepeat¶

Overview¶

The StringRepeat expression repeats a string a specified number of times by concatenating it with itself. It takes a string input and an integer count, returning a new string that contains the original string repeated the specified number of times.

Syntax¶

repeat(str, n)

// DataFrame API
col("column_name").repeat(n)

Arguments¶

Argument	Type	Description
str	StringTypeWithCollation	The input string to be repeated
times	IntegerType	The number of times to repeat the string

Return Type¶

Returns the same data type as the input string (str.dataType), which is a string type with collation support.

Supported Data Types¶

Input string: String types with collation support (including trim collation)
Input count: Integer type only
Implicit casting is supported through ImplicitCastInputTypes

Algorithm¶

Validates that both input expressions are not null (null intolerant behavior)
Casts the string input to UTF8String format internally
Casts the times parameter to Integer type
Calls the native repeat() method on the UTF8String object
Returns the concatenated result as a UTF8String

Partitioning Behavior¶

This expression does not affect partitioning behavior:

Preserves existing partitioning since it's a row-level transformation
Does not require shuffle operations
Can be applied within each partition independently

Edge Cases¶

Null handling: Returns null if either input argument is null (null intolerant)
Zero repetitions: Returns empty string when times = 0
Negative repetitions: Behavior depends on underlying UTF8String.repeat() implementation
Empty string input: Returns empty string regardless of repetition count
Large repetition counts: May cause memory issues or overflow depending on string length

Code Generation¶

This expression supports Tungsten code generation through the doGenCode method. It generates optimized code that directly calls the repeat() method on UTF8String objects, avoiding interpretation overhead.

Examples¶

-- Basic usage
SELECT repeat('123', 2);
-- Result: '123123'

-- With column reference
SELECT repeat(name, 3) FROM table;

-- Zero repetitions
SELECT repeat('abc', 0);
-- Result: ''

// DataFrame API usage
import org.apache.spark.sql.functions._

df.select(repeat(col("text_column"), 3))

// With literal values
df.select(repeat(lit("hello"), 2))