R help - Jul 2013 - ggplot2: Remove geom

Dear all,

Is there a possibility to remove a geom from a ggplot? Background suppose I have
a function which returns a ggplot object after some data re-formatting and
aggregation. While this ggplot object is fine in 90% of the cases it turns out
that for some cases I want to suppress one of the layers which was added to the
plot.

I could look at the source code of the function and write a new one, which has
an additional flag parameter, with which I could ask the function to add or not
to add the geom, but this sounds a bit of overkill to me and it would be nice,
if I could just remove the particular layer?

An example is in order to make my point clearer:

library(ggplot2)
d <- data.frame(x=rep(1:10, each = 10), y = rnorm(100), grp = rep(1:10, 10))

makePlot <- function() {
  ggplot(d, aes(x = x, y = y)) + stat_summary(fun.data =
"mean_cl_normal", color = "red") + geom_point()
}

(p <- makePlot())

## Now I want to have lines instead of points, but of course the points are
still there
p + geom_line(aes(group = grp, color = grp))

Again, it would not be difficult to rewrite makePlot to deal with that, but for
me this seems to be error prone / duplication. So ideally, I would like to do
something like:

p %-% geom_point()

which is ambiguous of course, as there can be several point layers in the plot.
Looking at

str(p)

I see that there is a layers slot, so I can do

q <- p
q$layers <- q$layers[-2]	
q + geom_line(aes(group = grp, color = grp))

which does actually what I want.

However, is there a way to do that in a more automated way? For now I have to
inspect the object and to decide which layer I want to delete, otherwise I can
get something like this:

makePlot2 <- function() {
  ggplot(d, aes(x = x, y = y)) + geom_point() + stat_summary(fun.data =
"mean_cl_normal", color = "red")
}
q <- makePlot2()
q$layers <- q$layers[-2]	
q + geom_line(aes(group = grp, color = grp))

which removes the error bars but not the points (as the order in layers
changed). So any ideas how to proceed in this case? If there is a nice way, I
could even think of overloading %-% which would fit nicely in the idea of a plot
which can not only be added layer by layer, but where I also could remove
certain layers.

Maybe (and even probable) there is a very good idea why I should not do that at
all and I would be curious to hear these things as well. For now I am yet
interested to know how I can remove layers of a plot conveniently.

Thanks for your help!

Kind Regards,

Thorn Thaler

On Mon, Jul 15, 2013 at 1:08 PM, Thaler,Thorn,LAUSANNE,Applied
Mathematics <Thorn.Thaler at rdls.nestle.com>
wrote:
> Dear all,
>
> Is there a possibility to remove a geom from a ggplot? Background suppose I
have a function which returns a ggplot object after some data re-formatting and
aggregation. While this ggplot object is fine in 90% of the cases it turns out
that for some cases I want to suppress one of the layers which was added to the
plot.
>
> I could look at the source code of the function and write a new one, which
has an additional flag parameter, with which I could ask the function to add or
not to add the geom, but this sounds a bit of overkill to me and it would be
nice, if I could just remove the particular layer?
>
> An example is in order to make my point clearer:
>
> library(ggplot2)
> d <- data.frame(x=rep(1:10, each = 10), y = rnorm(100), grp = rep(1:10,
10))
>
> makePlot <- function() {
>   ggplot(d, aes(x = x, y = y)) + stat_summary(fun.data =
"mean_cl_normal", color = "red") + geom_point()
> }
>
> (p <- makePlot())
>
> ## Now I want to have lines instead of points, but of course the points are
still there
> p + geom_line(aes(group = grp, color = grp))
>
> Again, it would not be difficult to rewrite makePlot to deal with that, but
for me this seems to be error prone / duplication. So ideally, I would like to
do something like:
>
> p %-% geom_point()
>
> which is ambiguous of course, as there can be several point layers in the
plot. Looking at
>
> str(p)
>
> I see that there is a layers slot, so I can do
>
> q <- p
> q$layers <- q$layers[-2]
> q + geom_line(aes(group = grp, color = grp))
>
> which does actually what I want.
>
> However, is there a way to do that in a more automated way? For now I have
to inspect the object and to decide which layer I want to delete, otherwise I
can get something like this:
>
> makePlot2 <- function() {
>   ggplot(d, aes(x = x, y = y)) + geom_point() + stat_summary(fun.data =
"mean_cl_normal", color = "red")
> }
> q <- makePlot2()
> q$layers <- q$layers[-2]
> q + geom_line(aes(group = grp, color = grp))
>
> which removes the error bars but not the points (as the order in layers
changed). So any ideas how to proceed in this case? If there is a nice way, I
could even think of overloading %-% which would fit nicely in the idea of a plot
which can not only be added layer by layer, but where I also could remove
certain layers.
>
> Maybe (and even probable) there is a very good idea why I should not do
that at all and I would be curious to hear these things as well. For now I am
yet interested to know how I can remove layers of a plot conveniently.
>
This seems to show which layer is which:
> sapply(p$layers, function(x) x$geom$objname)
[1] "pointrange" "point"


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