Create sequence of ggplots and send to pdf

Analysis background

See my previously posted tutorial Getting started with R, with plyr and ggplot2, for group by analysis. At the end of that tutorial we did some facet plots to show a bunch of histograms. What if we wanted to do a sequence of plots instead and save each of them to separate PDFs?

One approach Let’s get ggplot2 loaded…

library(ggplot2)

and the data file read in.

sched_df <- read.csv("data/SchedDaysAdv.csv")

Here’s the original facet plot of histograms of schedule lead time by service.

# Histogram with frequencies
ggplot(sched_df, aes(x = ScheduledDaysInAdvance)) + facet_wrap(~Service) + geom_histogram(aes(y = ..density..), 
    binwidth = 4)

We want a sequence of plots and to save each to its own PDF. Some Googling and StackOverflowing led me to the following approach using a custom function and lapply() for the “looping”.

doPlot = function(svc_name) {
    # Just get the records for this service
    temp_df = subset(sched_df, Service == svc_name)

    # Create the plot object
    ggobj = ggplot(temp_df, aes(x = ScheduledDaysInAdvance)) + geom_histogram(aes(y = ..density..), 
        binwidth = 4)

    # Add some titles and axis labels
    ggobj = ggobj + ggtitle(svc_name) + xlab("Scheduled Days in Advance") + 
        ylab("Frequency")

    # Need to use print() to actually produce the plot
    print(ggobj)

    # Save to PDF
    ggsave(sprintf("%s.pdf", svc_name))
}

Now we can use lapply() to apply our function to a list of unique service names. We can get those unique names with the unique() function. Done.

lapply(unique(sched_df$Service), doPlot)

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