stair function - how to

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I am not sure to understand your wish, do you mean something like:

sage: plot(floor, 0, 10)

You can use a sum of heaviside functions.

f(x)=heaviside(x)+heaviside(x-1)+heaviside(x-2)+heaviside(x-3)
plot(f(x),(x,0,4),exclude=[0,1,2,3])

Or, you can do it with a python function.

def step(x):
    if (0<x) and (x<1):
        return(1)
    elif (x<2):
        return(2)
    elif (x<3):
        return(3)
    else:
        return(4)
plot(lambda x: step(x),(x,0,4),exclude=[0,1,2,3])

You could also use the piecewise command.