finding closest value in an array

Question

int[] array = new int[5]{5,7,8,15,20};

int TargetNumber = 13;

For a target number, I want to find the closest number in an array. For example, whe

Answer 1

Performance wise custom code will be more useful.

public static int FindNearest(int targetNumber, IEnumerable collection) {
    var results = collection.ToArray();
    int nearestValue;
    if (results.Any(ab => ab == targetNumber))
        nearestValue = results.FirstOrDefault(i => i == targetNumber);
    else{
        int greaterThanTarget = 0;
        int lessThanTarget = 0;
        if (results.Any(ab => ab > targetNumber)) {
            greaterThanTarget = results.Where(i => i > targetNumber).Min();
        }
        if (results.Any(ab => ab < targetNumber)) {
            lessThanTarget = results.Where(i => i < targetNumber).Max();
        }

        if (lessThanTarget == 0) {
            nearestValue = greaterThanTarget;
        }
        else if (greaterThanTarget == 0) {
            nearestValue = lessThanTarget;
        }
        else if (targetNumber - lessThanTarget < greaterThanTarget - targetNumber) {
            nearestValue = lessThanTarget;
        }
        else {
            nearestValue = greaterThanTarget;
        }
    }
    return nearestValue;
}