r - Extract data from a ggplot

Question

I have made a plot using ggplot2 geom_histogram from a data frame. See sample below and link to the ggplot histogram Need to label each geom_vline with the factors using a nested ddply function and facet wrap

I now need to make a data frame that contains the summarized data used to generate the ggplot above.

Sector2 Family  Year    Length
BUN Acroporidae 2010    332.1300496
BUN Poritidae   2011    141.1467966
BUN Acroporidae 2012    127.479
BUN Acroporidae 2013    142.5940556
MUR Faviidae    2010    304.0405
MUR Faviidae    2011    423.152
MUR Pocilloporidae  2012    576.0295
MUR Poritidae   2013    123.8936667
NTH Faviidae    2010    60.494
NTH Faviidae    2011    27.427
NTH Pocilloporidae  2012    270.475
NTH Poritidae   2013    363.4635

Answer 1

To get values actually plotted you can use function ggplot_build() where argument is your plot.

p <- ggplot(mtcars,aes(mpg))+geom_histogram()+
      facet_wrap(~cyl)+geom_vline(data=data.frame(x=c(20,30)),aes(xintercept=x))

pg <- ggplot_build(p)

This will make list and one of sublists is named data. This sublist contains dataframe with values used in plot, for example, for histrogramm it contains y values (the same as count). If you use facets then column PANEL shows in which facet values are used. If there are more than one geom_ in your plot then data will contains dataframes for each - in my example there is one dataframe for histogramm and another for vlines.

head(pg$data[[1]])
  y count         x ndensity ncount density PANEL group ymin ymax
1 0     0  9.791667        0      0       0     1     1    0    0
2 0     0 10.575000        0      0       0     1     1    0    0
3 0     0 11.358333        0      0       0     1     1    0    0
4 0     0 12.141667        0      0       0     1     1    0    0
5 0     0 12.925000        0      0       0     1     1    0    0
6 0     0 13.708333        0      0       0     1     1    0    0
      xmin     xmax
1  9.40000 10.18333
2 10.18333 10.96667
3 10.96667 11.75000
4 11.75000 12.53333
5 12.53333 13.31667
6 13.31667 14.10000

head(pg$data[[2]])
  xintercept PANEL group xend  x
1         20     1     1   20 20
2         30     1     1   30 30
3         20     2     2   20 20
4         30     2     2   30 30
5         20     3     3   20 20
6         30     3     3   30 30