在r-月份中按年份对月度数据进行分面，没有数据出现

Question

I'm trying to create a grouped bar chart of monthly data, aggregated from daily data, over multiple years. I have accomplished what I wanted from my x-axis from faceting, using faceting as a way to apply a secondary sort (on year and month). Now that I've faceted by year, ggplot is showing all months - even when there's no data. This is wasting space and my actual data set has years of data and I want to add labels, so space is an issue.

How can I accomplish this without the wasted space? Is there a way to add the secondary sort (year,month) on the x-axis without faceting?

# create data set
date = seq(as.Date("2014-05-01"),as.Date("2015-05-10"), "day")
revenue = runif(375, min = 0, max = 200)
cost = runif(375, min = 0, max = 100)
df = data.frame(date,revenue,cost)
head(df)

# adding month and year column, then aggregating to monthly revenue and cost 
library(plyr)
df$month <- month(df$date, label=TRUE) 
df$year <- year(df$date) 
df <- as.data.frame(ddply(df, .(month,year), numcolwise(sum)))

# melting the data for a 'grouped chart' in ggplot
library(reshape)
df <-melt(df, id = c("month","year"))

#create chart
library(ggplot2)
g <-ggplot(df, aes(x=month, y=value, fill=variable)) 
g + geom_bar(stat="identity", position="dodge") + facet_wrap(~ year)

I feel certain that there's a more elegant way to do this from within ggplot. Am I right?

Answer 1

The key is to use scale = "free" in facet_wrap() . By following your code (with a revision), you'll see the graphic below.

set.seed(222)
date = seq(as.Date("2014-05-01"),as.Date("2015-05-10"), "day")
revenue = runif(375, min = 0, max = 200)
cost = runif(375, min = 0, max = 100)
mydf = data.frame(date,revenue,cost)

mydf$month <- month(mydf$date, label=TRUE) 
mydf$year <- year(mydf$date) 
mydf2 <- as.data.frame(ddply(mydf, .(month,year), numcolwise(sum)))

mydf3 <- melt(mydf2, id = c("month","year"))

ggplot(mydf3, aes(x=month, y=value, fill=variable)) +
geom_bar(stat = "identity", position = "dodge") +
facet_wrap(~ year, scale = "free")