Changing x axis label in GGPlot2

Question

I have an r data set which has money spendings spread across months, and also grouped by years.

Year|Mth_Year|Mth_Spend
2004|01-2004|42507163
2004|02-2004|3377592
2006|10-2006|3507636
2006|11-2006|4479139
2006|12-2006|2439603

I need to display the monthly information (grouped year wise), so that some quick comparisons can be done.

I am using the ggplot, geom_bar options to display the monthly spends. Below is the code, I use.

ggplot(data=yearly_spending,aes(x=Year,y=Mth_Spend,fill=Mth_Year))+
  geom_bar(stat="identity",color="black",position=position_dodge())+
  theme(axis.text.x=element_text(angle=90,hjust=1))

When I use this code, the bar chart is getting displayed. But in X Axis, only the years (2004, 2005 & 2006) are displayed. Can I get the months also displayed above the years. The years can appear horizontally, and while months can be placed vertically.

Answer 1

Thank you for all the suggestions. Using the scales package and lubridate to convert strings into date, I could solve the issue.

ggplot(data=monthly_spend_catwise,aes(x=Mth_Year,y=TotSpending,fill=Type))+
scale_x_date(labels=date_format("%m-%Y"),date_breaks = "1 month")+
theme(axis.text.x=element_text(angle=45,hjust=1,vjust=0.5))+
geom_bar(stat="identity",color="black",position=position_dodge())

I had formatted the dates in Mth_Year (instead of 01-2004, made it into 01-01-2004), using the below code.

spending$Mth_Year <- as.Date(paste("01",spending$Mth_Year,sep="-"),"%d-%m-%y")