Overriding tick labels in gnuplot

[Gnome]

1 down vote favorite

I have a text file containing data like this:

   Date          Hour          Data
2014/01/01        00            5
2014/01/01        01            10
2014/01/01        02            7
2014/01/01        03            6
.
.
.
2014/01/01        23            4
2014/01/02        00            6
2014/01/02        01            9
2014/01/02        02            2
.
.
.

I want to plot the file in gnuplot with "Data" on y axis and "Hour" on x axis which I know how to do that. I also want that when "Hour" value is "00" (or at the changing of dates) the related "Date" appears on the x axis instead of "Hour". any idea?

[Ethan Merritt]

plot 'info.dat' using 0:3:xtic(($2==0)?strcol(1):strcol(2))