Plotting multiple frequency polygon lines using ggplot2

Question

I have a dataset with records that have two variables: "time" which are id's of decades, and "latitude" which are geographic latitudes. I have 7 time periods (numbered from 26 to 32).

I want to visualize a potential shift in latitude through time. So what I need ggplot2 to do, is to plot a graph with latitude on the x-axis and the count of records at a certain latitude on the y-axis. I need it do this for the seperate time periods and plot everything in 1 graph.

I understood that I need the function freqpoly from ggplot2, and I got this so far:

qplot(latitude, data = lat_data, geom = "freqpoly", binwidth = 0.25)

This gives me the correct graph of the data, ignoring the time. But how can I implement the time? I tried subsetting the data, but I can't really figure out if this is the best way..

So basically I'm trying to get a graph with 7 lines showing the frequency distribution in each decade in order to look for a latitude shift.

Thanks!!

Answer 1

Without sample data it is hard to answer but try to add color=factor(time) (where time is name of your column with time periods). This will draw lines for each time period in different color.

qplot(latitude, data = lat_data, geom = "freqpoly", binwidth = 0.25,
                  color=factor(time))