3  Frequency polygons

Requirements:

✅ a numeric (continuous) variable


3.1 Description

A frequency polygon is a plot that displays data distributions using points connected by straight lines. It’s similar to a histogram but is more commonly used to compare data across multiple sets. A legend is often included to differentiate between various data sets. Frequency polygons are used to assess symmetry and skewness.

3.2 Set up

PACKAGES:

Install packages.

install.packages("palmerpenguins")
library(palmerpenguins) 
library(ggplot2)
library(dplyr) # for data manipulation

DATA:

Artwork by Allison Horst

The penguins data.

penguins <- palmerpenguins::penguins
glimpse(penguins)
#> Rows: 344
#> Columns: 8
#> $ species           <fct> Adelie, Adelie, Adelie…
#> $ island            <fct> Torgersen, Torgersen, …
#> $ bill_length_mm    <dbl> 39.1, 39.5, 40.3, NA, …
#> $ bill_depth_mm     <dbl> 18.7, 17.4, 18.0, NA, …
#> $ flipper_length_mm <int> 181, 186, 195, NA, 193…
#> $ body_mass_g       <int> 3750, 3800, 3250, NA, …
#> $ sex               <fct> male, female, female, …
#> $ year              <int> 2007, 2007, 2007, 2007…

3.3 Grammar

CODE:

  1. Create labels with labs()

  2. Initialize the graph with ggplot() and provide data

  3. Map flipper_length_mm to the x axis

  4. Add the geom_freqpoly() layer

labs_freqpoly <- labs(
  title = "Adult foraging penguins",
  subtitle = "Distribution of flipper length",
  x = "Flipper length (millimeters)")
ggp2_freqpoly <- ggplot(data = penguins,
      aes(x = flipper_length_mm)) + 
    geom_freqpoly()
ggp2_freqpoly + 
  labs_freqpoly

GRAPH:

Experiment to see how many bins fit your variable’s distribution.

show/hide 

ggp2_freqpoly_bins45 <- ggplot(data = penguins,
     aes(x = flipper_length_mm)) + 
     geom_freqpoly(bins = 45) 

ggp2_freqpoly_bins45 + 
  labs_freqpoly

ggp2_freqpoly_bins15 <- ggplot(data = penguins,
     aes(x = flipper_length_mm)) + 
     geom_freqpoly(bins = 15) 

ggp2_freqpoly_bins15 + 
  labs_freqpoly