Example plot from Burns et al. JAMA Network Open (2021)

Creating Nightingale rose diagram using ggplot (static figure)

  • This plot is also called Wind Rose and Coxcomb diagram.

  • This diagram was developed by Florence Nightingale (1820-1910), a statistician, nurse and social reformer who was the foundational philosopher of modern nursing.

  • For demonstration purpose, I will simulate a simple data inspired by the example figure.

  • Suppose we have three variables in our data

    • Year: 2016 to 2021
    • Instruments of health: physical, mental and social
    • my self-reported measure of health by instruments: a score between 1 and 5, where 5 represents the highest level of self-reported health
library(tidyverse)
library(DT)

set.seed(123)
dat <- tibble(
  Year = paste0("Y",rep(2016:2021, each=3)),
  Instrument = rep(c("physical","mental","social"),6),
  Score = sample(1:5, size = 3*6, replace = T))

dat %>% datatable(
  rownames = FALSE,
  options = list(
    columnDefs = list(list(className = 'dt-center', 
                      targets = 0:2))))

  • we plot year as our rays (or rose petals) and instruments as stacked bars with height representing the scores.

  • Adding labels on top of each ray. This step requires we position the label using angle degrees.

library(viridis)

p <- ggplot(dat) +  
  # Add the stacked bar
  geom_bar(aes(x=Year, y=Score, fill=Instrument), stat="identity", size=0.6, color="white") +
  scale_fill_viridis(discrete=TRUE, direction = 1, option = "C", name="Health Instrument") +
  ylim(0,15) + #using -1 as the lower bound to leave space in the centre of the polar
  coord_polar() +
  theme(
    panel.background = element_rect(fill = "white", colour = "white"),
    panel.grid.major = element_blank(),
    panel.grid.minor = element_blank(),
    panel.border = element_blank(),
    axis.line = element_blank(),
    axis.ticks = element_blank(),
    legend.position = "right",
    legend.text = element_text(size=18), #large font for website display
    legend.title = element_text(size=20), #large font for website display
    axis.text = element_blank(),
    axis.title = element_blank()) 

# Add labels on top of each bar
label_data <- dat %>% group_by(Year) %>% summarize(Tot=sum(Score))
angle= round(90 - 360 * (c(1:nrow(label_data))-0.5) /nrow(label_data),0)     # I substract 0.5 because the letter must have the angle of the centre of the bars. Not extreme right(1) or extreme left (0)
label_data$hjust<-ifelse(angle < -90, 1, 0)
label_data$angle<-ifelse(angle < -90, angle+180, angle)

p + geom_text(data=label_data, aes(x=Year, y=Tot+0.5, label=Year, hjust=hjust),
            color="black", size=6, angle= label_data$angle, inherit.aes = FALSE)

Creating interactive Nightingale rose diagram using plotly

  • In Plotly, r means radius and theta means angle. To specify categorical angle labels and ticks, we need to input character variable.

  • Because we specified theta to be categorical (representing variable Year), we need to define even breaks between 0 to 360 by the number of unique Years (6 years in this example) to place the angle labels.

    • This is controlled by setting period = 6 under the layout option of polar.

  • The interactive feature of plotly is super nice! You can try scaling and rotating the plot!

library(plotly)

fig <- plot_ly() %>%
  add_trace(
    data = dat,
    r = ~Score, #radius 
    theta = ~Year, #angle
    type="barpolar", 
    color = ~Instrument,
    hovertemplate = paste('Score: %{r}',
                        '<br>Year: %{theta}<br>')) %>%  
  layout(
    legend=list(title=list(text='Health Instrument')), 
    polar = list(angularaxis = list(
      rotation = 90,
      direction = 'clockwise', #position the polar diagram
      period = 6)), #evenly distribute angles to host categorical var;
    margin = 0.01) 
fig

R session information

## R version 4.0.5 (2021-03-31)
## Platform: x86_64-w64-mingw32/x64 (64-bit)
## Running under: Windows 10 x64 (build 19044)
## 
## Matrix products: 
## 
## locale:
## [1] LC_COLLATE=English_Canada.1252  LC_CTYPE=English_Canada.1252   
## [3] LC_MONETARY=English_Canada.1252 LC_NUMERIC=C                   
## [5] LC_TIME=English_Canada.1252    
## 
## attached base packages:
## [1] stats     graphics  grDevices utils     datasets  methods   base     
## 
## other attached packages:
##  [1] plotly_4.10.0     viridis_0.6.2     viridisLite_0.4.0 DT_0.21          
##  [5] forcats_0.5.1     stringr_1.4.0     dplyr_1.0.8       purrr_0.3.4      
##  [9] readr_2.1.2       tidyr_1.2.0       tibble_3.1.6      ggplot2_3.3.5    
## [13] tidyverse_1.3.1