Myujth

I'm fairly new to R and ggplot. I'm trying to plot a facet_wrap of a series of United States choropleth maps over the period 1999 - 2017.

I attempted to follow code from this post (How to map all the states of US using R with the number of crimes occurred in each state?) but am having trouble getting boundaries and filling in states with no data for a given year.

I have a data frame called by_year like such with data. The issue is for any one year, the majority of the states are not in the df (there was no value reported that year).

 state Year Value
new jersey 1999 13.8
 oklahoma 1999 16.5

The code I have so far is this:

us.states <- map_data("state")
ggplot(data = by_year, aes(map_id = state)) + 
 geom_map(aes(fill = Value), color= "black", map = us.states) + 
 expand_limits(x = us.states$long, y = us.states$lat) +
 coord_map() +
 scale_x_continuous(breaks = NULL) + scale_y_continuous(breaks = NULL) +
 labs(x = "", y = "") + theme(legend.position = "bottom", 
 panel.background = element_blank())+
 facet_wrap(~Year, ncol = 5)

This produces the following output:

As you can see, for any given year, many of the states do not have data. How to do I get outlines of the missing states for each year and fill them in in light gray? I was also hoping to change the color scale to shades of red (with darker shades being for higher values).

Thank you so much for any help.