How to plot an histogram with y as a sum of the x values for every bin in ggplot2

Question

I have a pv dataframe containing information regarding solar plants. One variable is the generation power in kw:

id   power
1    20.1
2    110.1
3    3.0
4    231.9
...  

I'm trying to plot an histogram with power as X values with a binwidth of 50 kW. As Y I would like to show the cumulative power for every plant in the range of the bin. I tried this code without success.

ggplot(pv, aes(x = power, y = sum(power)), stat = "bin") + 
    geom_histogram(stat = "identity", binwidth=50)

I need to calculate the sum by using the cut function or it is possible to generate this graph directly with ggplot2?

Answer 1

This should do what you want:

set.seed(1)
df <- data.frame(id=1:100, power=rlnorm(100, log(100)))
ggplot(df) + 
  geom_histogram(aes(x=power, weight=power), binwidth=50) +
  ylab("Total Power (kW)")

The weight aesthetic forces the stat calculation to multiply each count by the corresponding weight, which in this case is equivalent to summing the power values.

And here is a better visualization:

ggplot(transform(df, power.bin=cut(power, 0:24 * 50, include.lowest=TRUE))) + 
  geom_bar(aes(x=power.bin, y=power), color="white", position="stack", stat="identity") +
  ylab("Total Power (kW)") + 
  scale_x_discrete(drop=F) +
  theme(axis.text.x=element_text(angle=90, vjust=.5, hjust=1))