ggplot2: поле легенды обрезки

Question

Я сделал тепловую карту с geom_tile, содержащим эту легенду.

This is the code within ggplot() that I used:

scale_fill_gradient2(name = "log2(fold change)",
                             low = "navy",
                             mid = "white",
                             midpoint = 0,
                             high = "red",
                             breaks = c(-9,-8,-7,-6,-5,-4,-3,-2,-1,0,1,2,3,4),
                             limits = c(-9,5),
                             guide = guide_colorbar(frame.colour = "black", 
                                                    ticks.colour = "black",
                                                    barheight = 13.5))

In my current plot, it creates the legend and shows the colour gradient, ranging from -9 to 5. My question is how to crop the legend, so that it only shows the values ranging from -4 to 5, without changing the colour gradient ( как в этом примере ). Как этого добиться?