Plotting every second data point in ggplot2

I have the following dataset: ``` Data <- data.frame( week = c(1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4), variable = c("nuclear", "nuclear", "nuclear", "nuclear", "atomic", "atomic", "atomic", "atomic", "unemployment", "unemployment", "unemployment", "unemployment"), value = c(2, 3, 1, 4, 5, 1, 2, 3, 3, 2, 5, 1) ) ``` I need a black-white-graph. So I use the following code: ``` ggplot(Data, aes(week, value, group=variable)) + xlab("Year") + ylab("Frequency of searches") + geom_line(aes(linetype=variable))+ # Line type depends on cond geom_point(aes(shape=variable))+ # Shape depends on cond scale_shape_manual(values=c(0,1,2)) + # Change shapes scale_linetype_manual(values=c("solid", "dotted", "dotdash"))+ theme(legend.position="top", legend.title=element_blank(), panel.background = element_rect(fill = "#FFFFFF", colour="#000000"))+ stat_smooth(method="loess")) ``` That works for fine for this small dataset. But when it's bigger, it's difficult to distinguish the lines and points from each other. It all looks very similar. Is there a way to plot only every second or tenth data point?