R - ggplot2 - _line -为缺失值处理直线。

I have data that I am trying to plot. I have several variables that range from the years 1880-2012. I have one observation per year. But sometimes a variable does not have an observation for a number of years. For example, it may have an observation from 1880-1888, but then not from 1889-1955 and then from 1956-2012. I would like ggplot2 + geom_line to not have anything in the missing years (1889-1955). But it connects 1888 and 1956 with a straight line. Is there anything I can do to remove this line? I am using the ggplot function.I have data that I am trying to plot. I have se