[R] geom_ribbon removes missing values

[Paul Murrell]

Hi

grid.polygon() can do multiple polygons in a single call, but rather 
than using NA's to separate sub-polygons, it uses an 'id' argument (or 
an 'id.lengths' argument) to identify sub-polygons within the vectors of 
x- and y-values (see the examples in ?grid.polygon).  So a ggplot2 patch 
that makes use of that facility might make more sense.

Paul

On 6/7/2010 5:46 AM, Karsten Loesing wrote:
> Hi Hadley,
>
> On 5/31/10 9:51 PM, Hadley Wickham wrote:
>> There's no easy way to do this because behind the scenes geom_ribbon
>> uses grid.polygon.
>
> A possible workaround might be to have grid.polygon draw multiple
> polygons, one for each interval. We can do this by constructing vectors
> with coordinates for the first polygon, then NA, then coordinates for
> the second polygon, etc. Here are the vectors for my initial example:
>
> x<- c(x[1:4], x[4:1], NA, x[7:10], x[10:7])
> y<- c(ymax[1:4], ymin[4:1], NA, ymax[7:10], ymin[10:7])
>
> I worked on a simple (but ugly) patch to GeomRibbon in ggplot2 that does
> the job using an iteration:
>
>
> /Library/Frameworks/R.framework/Versions/2.10/Resources/library/ggplot2/R$
> diff ggplot2-orig ggplot2
> 5047,5048d5046
> <      data<- remove_missing(data, na.rm,
> <        c("x","ymin","ymax"), name = "geom_ribbon")
> 5050a5049,5069
>>      start<- 0
>>      polyx<- c()
>>      polyy<- c()
>>      for (i in 1:(length(data$x)+1)) {
>>        if (i>  length(data$x) || is.na(data$ymin[i]) ||
>>            is.na(data$ymax[i])) {
>>          if (start>  0) {
>>            polyx<- c(polyx, data$x[start:(i-1)],
>>                data$x[(i-1):start], NA)
>>            polyy<- c(polyy, data$ymax[start:(i-1)],
>>                data$ymin[start:(i-1)], NA)
>>            start<- 0
>>          }
>>        } else {
>>          if (start == 0) {
>>            start<- i
>>          }
>>        }
>>      }
>>      polyx<- head(polyx, length(polyx) - 1)
>>      polyy<- head(polyy, length(polyy) - 1)
> 5052c5071
> <        coordinates$munch(data.frame(x=c(x, rev(x)), y=c(ymax,
> rev(ymin))), scales)
> ---
>>        coordinates$munch(data.frame(x = polyx, y = polyy), scales)
>
>
> Do you like the described approach? Can you help me make my patch better?
>
> In particular, I'd want to avoid iterating over the data frame and
> extract start and end index of intervals separated by NA. Is there a
> function for this or at least a better approach?
>
> Also, probably a stupid question: How do I tell R to use the cloned
> ggplot2 sources instead of the installed ggplot2 package? As you can
> see, I modified the installed package, but I'd rather work with Git here.
>
> Thanks,
> --Karsten
>
>
>> On Sun, May 30, 2010 at 7:26 AM, Karsten Loesing
>> <karsten.loesing at gmx.net>  wrote:
>>> Hi everyone,
>>>
>>> it looks like geom_ribbon removes missing values and plots a single
>>> ribbon over the whole interval of x values. However, I'd rather want it
>>> to act like geom_line, that is, interrupt the ribbon for the interval of
>>> missing values and continue once there are new values. Here's an example:
>>>
>>> library(ggplot2)
>>> df<- data.frame(
>>>   date = seq(from = as.Date("2010-05-15"),
>>>              to = as.Date("2010-05-24"),
>>>              by = "1 day"),
>>>   low = c(4, 5, 4, 5, NA, NA, 4, 5, 4, 5),
>>>   mid = c(8, 9, 8, 9, NA, NA, 8, 9, 8, 9),
>>>   high = c(12, 13, 12, 13, NA, NA, 12, 13, 12, 13))
>>> ggplot(df, aes(x = date, y = mid, ymin = low, ymax = high)) +
>>>   geom_line() +
>>>   geom_ribbon(fill = alpha("blue", 0.5))
>>>
>>> When running this code, R tells me:
>>>
>>> Warning message:
>>> Removed 2 rows containing missing values (geom_ribbon).
>>>
>>> When you look at the graph, you can see that the line stops at May 18
>>> and starts again on May 21. But the ribbon reaches from May 15 to 24,
>>> even though there are no values on May 19 and 20.
>>>
>>> Is there an option that I could set? Or a geom/stat that I should use
>>> instead? In my pre-ggplot2 times I used polygon(), but I figured there
>>> must be something better in ggplot2 (as there has always been so far).
>>>
>>> Thanks,
>>> --Karsten
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>>
>>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
Private Bag 92019
Auckland
New Zealand
64 9 3737599 x85392
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/