participantsByDay(s)

function participantsByDay(s)
d = [s.date];
authorBins = floor(d(1)):1:ceil(d(end));
authorCount = zeros(size(authorBins));
for i = 1:length(authorBins)-1;
    thisBin = s((authorBins(i)<=[s.date]) & ([s.date] < authorBins(i+1)));
    authorCount(i) = length(unique({thisBin.author}));
end
nonempty = find(authorCount ~= 0);
range = min(nonempty):max(nonempty);

clf
drawnow
bar(authorBins(range)+(authorBins(2)-authorBins(1))/2,authorCount(range),'FaceColor','b','EdgeColor','b')
box on
datetick
hold on
set(gca,'GridLineStyle','-')
xlabel('day')
ylabel('unique participants')
title('Participation by Day')