[R] ggplot: combining geom's in function

[Jeff Newmiller]

If you want to use the lattice way of doing things, why are you using ggplot?

`+` is defined for the output of ggplot (class "waiver") on the left, and the output of a layer function ("proto") on the right. The design of ggplot assumes left-to-right evaluation, which your first attempt failed to maintain. Your second approach is how I usually add multiple layers to a plot.
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Sent from my phone. Please excuse my brevity.

On October 23, 2015 9:46:49 PM GMT+02:00, sbihorel <Sebastien.Bihorel at cognigencorp.com> wrote:
>Following up on my previous reply, this following would work but would 
>not behave like a geom function:
>
>geom_xyplot <- function (gplot, mapping = NULL, data = NULL, stat = 
>"identity",
>                          position = "identity", na.rm = FALSE, type = 
>'p', ...) {
>
>   if (any(type=='p')){
>     gplot + geom_point(mapping = mapping, data = data, stat = stat,
>                        position = position, na.rm = na.rm, ...)
>   }
>   if (any(type=='l')){
>     gplot + geom_path(mapping = mapping, data = data, stat = stat,
>                       position = position, na.rm = na.rm, ...)
>   }
>   if (any(type%in%c('b','o'))){
>     gplot + geom_point(mapping = mapping, data = data, stat = stat,
>                        position = position, na.rm = na.rm, ...) +
>       geom_path(mapping = mapping, data = data, stat = stat,
>                 position = position, na.rm = na.rm, ...)
>   }
>}
>
>Sebastien
>
>On 10/23/2015 12:27 PM, Jeff Newmiller wrote:
>> Have you looked at the qplot function in the ggplot2 package?
>>
>---------------------------------------------------------------------------
>> Jeff Newmiller                        The     .....       .....  Go
>Live...
>> DCN:<jdnewmil at dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live
>Go...
>>                                        Live:   OO#.. Dead: OO#.. 
>Playing
>> Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
>> /Software/Embedded Controllers)               .OO#.       .OO#. 
>rocks...1k
>>
>---------------------------------------------------------------------------
>> Sent from my phone. Please excuse my brevity.
>>
>> On October 23, 2015 3:12:41 PM GMT+02:00, sbihorel
><Sebastien.Bihorel at cognigencorp.com> wrote:
>>> Hi,
>>>
>>> Next adventure into my journey from lattice to ggplot: I would like
>to
>>> create a custom generic function that combines multiple existing
>geom's
>>>
>>> in order to reproduce what the lattice panel.xyplot function does
>based
>>>
>>> on the type argument (ie, plotting points only for type='p',
>plotting
>>> lines for type 'l', etc).
>>>
>>> My current naive attempt is:
>>>
>>> library(lattice)
>>> library(ggplot2)
>>>
>>> geom_xyplot <- function (mapping = NULL, data = NULL, stat =
>>> "identity",
>>>                           position = "identity", na.rm = FALSE, type
>=
>>> 'p', ...) {
>>>
>>>    if (any(type=='p')){
>>>      geom_point(mapping = mapping, data = data, stat = stat,
>>>                 position = position, na.rm = na.rm, ...)
>>>    }
>>>    if (any(type=='l')){
>>>      geom_path(mapping = mapping, data = data, stat = stat,
>>>                position = position, na.rm = na.rm, ...)
>>>    }
>>>    if (any(type%in%c('b','o'))){
>>>      geom_point(mapping = mapping, data = data, stat = stat,
>>>                 position = position, na.rm = na.rm, ...) +
>>>        geom_path(mapping = mapping, data = data, stat = stat,
>>>                  position = position, na.rm = na.rm, ...)
>>>    }
>>> }
>>>
>>> data <- data.frame(x = rep(1:4, each = 25),
>>>                     y = rep(1:25, times = 4),
>>>                     g = rep(1:4, each = 25))
>>> data$x <- data$x + 0.005*(data$y)^2-0.1*data$y+1
>>>
>>> ggplot(data2, aes(x, y, group = g, colour = factor(g))) +
>>> geom_xyplot(type = 'l')
>>>
>>> I get:
>>>> Error: No layers in plot
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