[R] ggplot: add points selectively to curves

[arun]

Hi,
May be this helps:
gg <- ggplot(plotdat, aes(x = Age, y = Probability, color = Level)) + geom_line(size=2.5) + theme_bw() + xlim(10,80) + facet_grid(Sex ~ Treatment, # scales = "free", labeller = function(x, y) sprintf("%s = %s", x, y) ) 

plotdat2 <- subset(plotdat,as.character(Improved)==as.character(Level)) 


gg+geom_point(data= plotdat2, aes(x=Age, y=Probability),color="black",size=1.5)


A.K.


On Wednesday, April 2, 2014 9:22 PM, Michael Friendly <friendly at yorku.ca> wrote:
Thanks, Dennis

Not quite.  I need to have the same lines as in the original, using 
plotdat, but then
add the points from your plotdat2

gg <- ggplot(plotdat, aes(x = Age, y = Probability, color = Level)) +
     geom_line(size=2.5) + theme_bw() + xlim(10,80) +
#    geom_point(color="black", size=1.5) +         # not these points
     facet_grid(Sex ~ Treatment, # scales = "free",
                labeller = function(x, y) sprintf("%s = %s", x, y)
                )

# want these points, added to the above plot
plotdat2 <- subset(plotdat,
                      as.character(Improved) == as.character(Level))



On 02/04/2014 7:09 PM, Dennis Murphy wrote:
> Hi Michael:
>
> Does this work?
>
> plotdat2 <- subset(plotdat,
>                       as.character(Improved) == as.character(Level))
> ggplot(plotdat2, aes(x = Age, y = Probability, color = Level)) +
>      geom_line(size=2.5) + theme_bw() + xlim(10,80) +
>      geom_point(color="black", size=1.5) +
>      facet_grid(Sex ~ Treatment,
>                 labeller = function(x, y) sprintf("%s = %s", x, y)
>                 )
>
> Dennis
>
> On Wed, Apr 2, 2014 at 7:43 AM, Michael Friendly <friendly at yorku.ca> wrote:
>> I'm working on an example of plotting predicted probabilities from a
>> proportional odds model.
>> The steps below generate a data frame, plotdat, that I want to plot with
>> ggplot.
>>
>> library(MASS)
>> data("Arthritis", package="vcd")
>> arth.polr <- polr(Improved ~ Sex + Treatment + Age, data=Arthritis,
>> Hess=TRUE)
>>
>> # get predicted probs for categories of Improve
>> arth.fitp <- cbind(Arthritis,
>>                    predict(arth.polr, type="probs"))
>> head(arth.fitp)
>>
>> # reshape probs to long
>> library(reshape2)
>> plotdat <- melt(arth.fitp,
>>                  id.vars = c("Sex", "Treatment", "Age", "Improved"),
>>                  measure.vars=c("None", "Some", "Marked"),
>>                  variable.name = "Level",
>>                  value.name = "Probability")
>> ## view first few rows
>> head(plotdat)
>>
>>> head(plotdat)
>>     Sex Treatment Age Improved Level Probability
>> 1 Male   Treated  27     Some  None   0.7326185
>> 2 Male   Treated  29     None  None   0.7174048
>> 3 Male   Treated  30     None  None   0.7096042
>> 4 Male   Treated  32   Marked  None   0.6936286
>> 5 Male   Treated  46   Marked  None   0.5702499
>> 6 Male   Treated  58   Marked  None   0.4563432
>>
>> In the plot step, I am plotting Probability vs. Age, stratified by Level,
>> and faceted by
>> Sex and Treatment.  My question concerns the use of geom_point().
>> The call below plots 3 points for each case, one on each Level curve.
>>
>>
>> ggplot(plotdat, aes(x = Age, y = Probability, color = Level)) +
>>      geom_line(size=2.5) + theme_bw() + xlim(10,80) +
>>      geom_point(color="black", size=1.5) +
>>      facet_grid(Sex ~ Treatment,
>>                 labeller = function(x, y) sprintf("%s = %s", x, y)
>>                 )
>>
>> Instead,
>> I want to plot only one point for each case, for the value of Level that
>> corresponds
>> to the value of Improved in this data set.  Somehow, this involves something
>> like an aes() argument to geom_point(), with Level indexed by Improved, or
>> some such.
>> How can I do this?
>>
>> --
>> Michael Friendly     Email: friendly AT yorku DOT ca
>> Professor, Psychology Dept. & Chair, Quantitative Methods
>> York University      Voice: 416 736-2100 x66249 Fax: 416 736-5814
>> 4700 Keele Street    Web:  http://www.datavis.ca
>> Toronto, ONT  M3J 1P3 CANADA
>>
>> ______________________________________________
>> 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.


-- 
Michael Friendly     Email: friendly AT yorku DOT ca
Professor, Psychology Dept. & Chair, Quantitative Methods
York University      Voice: 416 736-2100 x66249 Fax: 416 736-5814
4700 Keele Street    Web:  http://www.datavis.ca
Toronto, ONT  M3J 1P3 CANADA

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and provide commented, minimal, self-contained, reproducible code.