[R] Missing shapes in legend with scale_shape_manual

[Howard, Tim G (DEC)]

I believe the missing shapes are because you had set alpha=0 for the last geom point. 

I expect there are better ways, but one way to handle it would be to avoid the filtering, adding columns with med and exercise status, like the following:

# setup with data provided
Date <- c('2023-10-17', '2023-10-16', '2023-10-15', '2023-10-14',
         '2023-10-13', '2023-10-12', '2023-10-11')
Time <- c('08:50', '06:58', '09:17', '09:04', '08:44', '08:55', '07:55') 
bg <- c(128, 144, 137, 115, 136, 122, 150)
missed_meds <- c(TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, TRUE)
no_exercise <- c(FALSE, FALSE, TRUE, FALSE, TRUE, TRUE, TRUE)

b2 <- data.frame(Date, Time, bg, missed_meds, no_exercise)

b2$Date <- as.Date(b2$Date)
# add "status" columns, could also be defined as factor. 
b2$medStat <- c("missed_meds",NA, NA, NA, NA, NA, "missed_meds")
b2$exercise <- c(NA, NA, "missed_exercise",NA,"missed_exercise", "missed_exercise", "missed_exercise")

Then your ggplot call would be like this:

ggplot(data = b2, aes(x = Date, y = bg)) +
  geom_line() +
  geom_point(aes(shape = medStat), size = 3)+
  geom_point(aes(shape = exercise),size = 3)+
  scale_y_continuous(name = "Blood glucose (mg/dL)",
                     breaks = seq(100, 230, by = 20)
  ) +
  geom_hline(yintercept = 130) +
  scale_shape_manual(name = "Conditions",
                     labels = c("Missed meds",
                                "Missed exercise"),
                     values = c(20, 4)
  )


Note that this method then gets very close without the scale_shape_manual, too. 

Hope that helps. 
Tim


> Date: Mon, 30 Oct 2023 20:55:17 +0000
> From: Kevin Zembower <kevin using zembower.org>
> To: r-help using r-project.org <r-help using r-project.org>
> Subject: [R] Missing shapes in legend with scale_shape_manual
> Message-ID:
>         <0100018b825e8f7f-646d2539-f8b5-4e1a-afc3-5d29f961967f-
> 000000 using email.amazonses.com>
> 
> Content-Type: text/plain; charset="utf-8"
> 
> Hello,
> 
> I'm trying to plot a graph of blood glucose versus date. I also record
> conditions, such as missing the previous night's medications, and missing
> exercise on the previous day. My data looks like:
> 
> > b2[68:74,]
> # A tibble: 7 × 5
>   Date       Time      bg missed_meds no_exercise
>   <date>     <time> <dbl> <lgl>       <lgl>
> 1 2023-10-17 08:50    128 TRUE        FALSE
> 2 2023-10-16 06:58    144 FALSE       FALSE
> 3 2023-10-15 09:17    137 FALSE       TRUE
> 4 2023-10-14 09:04    115 FALSE       FALSE
> 5 2023-10-13 08:44    136 FALSE       TRUE
> 6 2023-10-12 08:55    122 FALSE       TRUE
> 7 2023-10-11 07:55    150 TRUE        TRUE
> >
> 
> This gets me most of the way to what I want:
> 
> ggplot(data = b2, aes(x = Date, y = bg)) +
>     geom_line() +
>     geom_point(data = filter(b2, missed_meds),
>                shape = 20,
>                size = 3) +
>     geom_point(data = filter(b2, no_exercise),
>                shape = 4,
>                size = 3) +
>     geom_point(aes(x = Date, y = bg, shape = missed_meds),
>                alpha = 0) + #Invisible point layer for shape mapping
>     scale_y_continuous(name = "Blood glucose (mg/dL)",
>                        breaks = seq(100, 230, by = 20)
>                        ) +
>     geom_hline(yintercept = 130) +
>     scale_shape_manual(name = "Conditions",
>                        labels = c("Missed meds",
>                                   "Missed exercise"),
>                        values = c(20, 4),
>                        ## size = 3
>                        )
> 
> However, the legend just prints an empty square in front of the labels.
> What I want is a filled circle (shape 20) in front of "Missed meds" and a filled
> circle (shape 4) in front of "Missed exercise."
> 
> My questions are:
>  1. How can I fix my plot to show the shapes in the legend?
>  2. Can my overall plotting method be improved? Would you do it this way?
> 
> Thanks so much for your advice and guidance.
> 
> -Kevin
> 
> 
> 
>