How to number the peaks and troughs of signal ?

numPoints = 50;
x = sort(rand(1, numPoints));
y = rand(1, numPoints);
plot(x, y, 'k-', 'LineWidth', 2);
grid on;
[peakValues, indexesOfPeaks] = findpeaks(y);
hold on;
peakx = x(indexesOfPeaks);
peaky = y(indexesOfPeaks);
plot(peakx, peaky, 'r*', 'LineWidth', 2, 'MarkerSize', 10);
% Find valleys on inverted signal
[valleyValues, indexesOfValleys] = findpeaks(-y);
valleyx = x(indexesOfValleys);
valleyy = y(indexesOfValleys);
hold on;
plot(valleyx, valleyy, 'b*', 'LineWidth', 2, 'MarkerSize', 10);