Change bar graph color by sign

I have a 502x2 column matrix made up of B = [datenum, data]. There are positive nad negative data values, and I want to make all of the positive values red and all of the negative values blue, similar to the figure midway down this page: https://niwa.co.nz/climate/information-and-resources/southern-annular-mode

My code so far is just:

bar(B(:,1), B(:,2))

Is there a straightforward way to do this?

Thank you!

Answer 1

[Karthik Ravishankar]

bar(B(B(:,2)>=0,1), B(B(:,2)>=0,2),'FaceColor','b')

hold on

bar(B(B(:,2)<0,1), B(B(:,2)<0,2),'FaceColor','r')

[Lutrinae]

Thank you!

Answer 2

[David Hill]

x=B(:,1)';
y=B(:,1)';
b=bar(x,y,'r');
b.FaceColor='Flat';
b.CData(y<0,:)=repmat([0 0 1],nnz(y<0),1);