How to create Quadrant Plots in R

Quadrant Plot Data

# Load the data
data(iris)
head(iris)

##   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
## 1          5.1         3.5          1.4         0.2  setosa
## 2          4.9         3.0          1.4         0.2  setosa
## 3          4.7         3.2          1.3         0.2  setosa
## 4          4.6         3.1          1.5         0.2  setosa
## 5          5.0         3.6          1.4         0.2  setosa
## 6          5.4         3.9          1.7         0.4  setosa

Data Processing

# Calculate midpoints for the x-axis and y-axis
x_mid <- mean(c(max(iris$Petal.Length, na.rm = TRUE), min(iris$Petal.Length, na.rm = TRUE)))
y_mid <- mean(c(max(iris$Petal.Width, na.rm = TRUE), min(iris$Petal.Width, na.rm = TRUE)))

# Create a new column 'quadrant' in the iris data
iris2 <- iris %>% mutate(quadrant = case_when(
  Petal.Length > x_mid & Petal.Width > y_mid ~ "Q1",
  Petal.Length <= x_mid & Petal.Width > y_mid ~ "Q2",
  Petal.Length <= x_mid & Petal.Width <= y_mid ~ "Q3",
  TRUE ~ "Q4"
))

head(iris2)

##   Sepal.Length Sepal.Width Petal.Length Petal.Width Species quadrant
## 1          5.1         3.5          1.4         0.2  setosa       Q3
## 2          4.9         3.0          1.4         0.2  setosa       Q3
## 3          4.7         3.2          1.3         0.2  setosa       Q3
## 4          4.6         3.1          1.5         0.2  setosa       Q3
## 5          5.0         3.6          1.4         0.2  setosa       Q3
## 6          5.4         3.9          1.7         0.4  setosa       Q3

Summary Table

# Create a summary table 'iris_labels'
iris_labels <- iris2 |> 
  count(quadrant) |> 
  mutate(x = if_else(quadrant %in% c("Q1", "Q4"), Inf, -Inf),
         hjust = if_else(quadrant %in% c("Q1", "Q4"), 1, 0),
         y = if_else(quadrant %in% c("Q1", "Q2"), Inf, -Inf),
         vjust = if_else(quadrant %in% c("Q1", "Q2"), 1, 0))
head(iris_labels)

##   quadrant  n    x hjust    y vjust
## 1       Q1 71  Inf     1  Inf     1
## 2       Q2  1 -Inf     0  Inf     1
## 3       Q3 60 -Inf     0 -Inf     0
## 4       Q4 18  Inf     1 -Inf     0

Quadrant Plot

# Create a scatter plot with quadrant color-coding
ggplot(iris2, aes(x = Petal.Length, y = Petal.Width, color = quadrant)) +
    geom_vline(xintercept = x_mid) +
    geom_hline(yintercept = y_mid) +
    geom_point() +
    # Add labels to the plot based on the summary table 'iris_labels'
    geom_label(data = iris_labels,
               aes(label = paste0("n = ", n),
                   x = x, y = y, color = NULL,
                   hjust = hjust, vjust = vjust),
               fill = NA, label.size = 0,
               show.legend = FALSE) +
    labs(title = "Quadrant Plot of Iris Data",
         x = "Petal Length",
         y = "Petal Width")

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