CODEWITHSUNDEEP
rggplot2geom-hline
damo
damo

Reputation: 473

Adding a horizontal line to a scatterplot in ggplot2

Following on from this How to add the results of applying a function to an existing data frame?

library (tidyverse)
library (epitools)


# here's my made up data

DISEASE = c("Marco Polio","Marco Polio","Marco Polio","Marco Polio","Marco Polio",
            "Mumps","Mumps","Mumps","Mumps","Mumps",
            "Chicky Pox","Chicky Pox","Chicky Pox","Chicky Pox","Chicky Pox")
YEAR = c(2011, 2012, 2013, 2014, 2015,
         2011, 2012, 2013, 2014, 2015,
         2011, 2012, 2013, 2014, 2015)
VALUE = c(82,89,79,51,51,
          79,91,69,89,78,
          71,69,95,61,87)
AREA =c("A", "B","C")

DATA = data.frame(DISEASE, YEAR, VALUE,AREA)


DATA %>%
    mutate(POPN = case_when(
        AREA == "A" ~ 2.5,
        AREA == "B" ~ 3,
        AREA == "C" ~ 7,
        TRUE ~ 0)) %>%
    group_by(DISEASE,AREA,POPN) %>%
    count(AREA) %>%
    mutate(res = list(pois.byar(n, POPN))) %>%
    unnest()

gives me what I need.

What I'd like to do is plot this on a scatter plot with a horizontal line equal to one of the rates I've calculated. Rather than adding it manually.

I thought this might work

DATA%>%filter(DISEASE== "Chicky Pox")%>%
  ggplot(aes(x=AREA, y=rate)) +geom_point() +
  geom_hline(yintercept=20, linetype="dashed", color = "red")

Which it does. It gives me a line at 20. But how could I make it give me a line equal to the value of rate for area A (for example). This way you could quickly see which rates were above or below the rate of A.

Again. Apologies, this is simple. But it's late...

Upvotes: 1

Views: 933

Answers (1)

Marius
Marius

Reputation: 60070

You can put some simple subsetting conditions in aes(), which means this is pretty straightforward as long as the conditions aren't too complex:

DATA %>%
    filter(DISEASE== "Chicky Pox") %>%
    ggplot(aes(x=AREA, y=rate)) +
    geom_point() +
    geom_hline(aes(yintercept=rate[AREA == "A"]), 
               linetype="dashed", color = "red")

Upvotes: 1

Related Questions