/**
 * Given an array and a number N, return a new array which contains every nTh
 * element of the input array. For n below 1, an empty array is returned.
 * If isValid is provided, all candidates must suffice the condition, else undefined is returned.
 * @param {T[]} array An input array.
 * @param {integer} n A number
 * @param {Function} isValid A function to evaluate a candidate form the array
 * @returns {T[]} The result array of the same type as the input array.
 */
export declare function getEveryNthWithCondition<Type>(array: ReadonlyArray<Type>, n: number, isValid?: (candidate: Type) => boolean): ReadonlyArray<Type> | undefined;