# Manage x-axis using ggplot()

Here is my data prep.

NEI <- readRDS("summarySCC_PM25.rds")
Baltimore <- NEI[NEI$fips=="24510", ] Baltimore$type <- as.factor(Baltimore$type) Total_Emmisssions <- aggregate(Baltimore$Emissions,
by=list(Baltimore$year, Baltimore$type),
FUN=sum)
names(Total_Emmisssions) <- c("Year","Type","Emissions")


Plot code

library(ggplot2)
g <- ggplot(Total_Emmisssions,aes(x=Year, y=Emissions, colour=Type))
g1 <- g+geom_point()
g2 <- g1+facet_grid(. ~ Type)
g3 <- g2+geom_smooth(method="lm", se=FALSE)


However, in this plot, the year is always 2002-2008. How do I change the scale / ticks to show from 1999-2008 at an interval of 3 years. Using scale_x_discrete does not work and it messes the graph. Please help.

str(Total_Emmisssions)
'data.frame':   16 obs. of  3 variables:
$Year : int 1999 2002 2005 2008 1999 2002 2005 2008 1999 2002 ...$ Type     : Factor w/ 4 levels "NON-ROAD","NONPOINT",..: 1 1 1 1 2 2 2 2 3 3 ...
\$ Emissions: num  522.9 240.8 248.9 55.8 2107.6 ...


Change Year to a factor and add group=1:
g <- ggplot(Total_Emmisssions,aes(x=factor(Year), y=Emissions, colour=Type, group=1))

you can leave the rest the same (you'll also prbly want to change the xlab).
• How does the geom_smooth() continue to work? I mean, for a line to fit, I was of the understanding that there needs t be two set of numbers. In this case, I don't understand how a factor and a number can come to give a linear regression model line. Or may be I just don't understand it to begin with.