Compare two numeric variables by two groups

Question

How I can build ggplot2 graph with two numeric variables on x axis as mean and sd, by two groups? As an example: on the left hand preoperative Hb value, by 2 groups and on the right the postoperative Hb values by the same 2 groups.

Answer 1

Is this similar to what you're looking for?

library(tidyverse)
library(reshape2)

# creating some nonsense sample data
x <- iris %>%
  select(-Petal.Width,-Sepal.Width) %>%
  melt(id.vars="Species") %>%
  group_by_at(colnames(select_if(.,negate(is.numeric)))) %>%
  summarise_all(mean,na.rm=T) %>%
  mutate(sd01=value-value/10,
         sd02=value+value/10) %>%
  rename(mean=value,
         groups=variable)

# plotting
ggplot(x,aes(Species,mean,color=Species))+
  geom_point(stat="identity")+
  geom_errorbar(aes(ymin=sd01,ymax=sd02))+
  facet_wrap(~groups, strip.position = "bottom")+
  theme(axis.ticks = element_blank(),
        strip.background = element_blank(),
        strip.text.x = element_text(),
        panel.spacing = unit(0, "lines"))+
  scale_y_continuous(expand=c(0,0))+
  annotate("segment", x = 0, y = 0, xend = 4, yend = 0)

EDIT: using geom_pointrange() makes the code shorter and changes the look of the errorbar.

ggplot(x,aes(Species,mean,color=Species))+
  geom_pointrange(aes(ymin=sd01,ymax=sd02),stat="identity")+
  facet_wrap(~groups, strip.position = "bottom")+...