ggplot facets of plots of sum of data, rather than data itself

Question

I'm trying to produce a plot of sums of a particular variable over time by facet in ggplot. I'm working on a school assignment, so I will use the built-in mpg data set for this question rather than the actual data.

One task is to plot the displacement by year for each class in mpg. The code

qplot(data = mpg, year, displ, facets = . ~ class)

produces the desired result. But for the next question, I have to produce nearly the same plot but plot the sum of the displacements by year for each class, and I can't seem to do it. I've tried variations of tapply to no avail. I had hoped that

qplot(data = mpg, year, sum(displ), facets = . ~ class)

would do it but it did not.

you need to change the data fed to qplot with tapply or with group_by from dplyr for example. — Haboryme, Jan 29 '17 at 14:50

score 1 · Accepted Answer · answered Jan 29 '17 at 16:23

1

You could consider using stat_summary and skipping qplot:

ggplot(mpg, aes(x=year, y = displ)) +
  stat_summary(fun.y="sum", geom="point") + facet_grid(.~class)

answered Jan 29 '17 at 16:23

Heroka

12,889
1
28
38

score 0 · Answer 2 · answered Jan 29 '17 at 19:19

0

We could try this with dplyr too:

library(dplyr)
mpg %>% group_by(year, class) %>% summarise(displ=sum(displ)) %>% 
  ggplot(aes(year, displ)) + geom_point() + facet_grid(~class)

answered Jan 29 '17 at 19:19

Sandipan Dey

21,482
2
51
63

ggplot facets of plots of sum of data, rather than data itself

2 Answers2