sum

Returns the sum of all elements in the array. sumBy variants allow mapping each element through a selector function before summing, supporting Int, Double, ComplexFloat, and ComplexDouble result types.

Signatures

fun <T : Number, D : Dimension> MultiArray<T, D>.sum(): T

inline fun <T : Number, D : Dimension> MultiArray<T, D>.sumBy(
    selector: (T) -> Int
): Int

inline fun <T : Number, D : Dimension> MultiArray<T, D>.sumBy(
    selector: (T) -> Double
): Double

Parameters

Parameter	Type	Description
`selector`	`(T) -> Int`	Maps each element to an `Int` before summing.
`selector`	`(T) -> Double`	Maps each element to a `Double` before summing.

Returns: The sum of all elements (or transformed elements).

Example

val a = mk.ndarray(mk[1, 2, 3, 4, 5])

a.sum()                      // 15
a.sumBy { it * it }          // 55 (sum of squares)

val b = mk.ndarray(mk[1.5, 2.5, 3.0])
b.sum()                      // 7.0

28 February 2026