How to store multiple "RiseTime" data from a step(sys) in a vector from a graph in Matlab GUI ?

Every time I press "pushbutton1" I'm getting a new step response on the same graph. So for every response, I need to take the "RiseTime" and store it into a vector. Then compare each value of "RiseTime" and find the lowest one.

%displaying the rise time in editbox named "rt"

rise_time= stepResults.RiseTime

set(handles.rt, 'String', rise_time)

%getting the value of the risetime

x = str2num(get(handles.rt,'String'))

With this code, I can only take the value of rising time of the last step(sys). But I want to get all the values so in the end I can compare them and find the lowest one and display it to the user of the interface.