13  Relationships

Regression, smoothing, density estimation, and heatmaps — revealing structure between two variables.

(ns napkinsketch-book.relationships
  (:require
   ;; Shared datasets for these docs
   [napkinsketch-book.datasets :as data]
   ;; Kindly — notebook rendering protocol
   [scicloj.kindly.v4.kind :as kind]
   ;; Napkinsketch — composable plotting
   [scicloj.napkinsketch.api :as sk]
   ;; Fastmath — random number generation
   [fastmath.random :as rng]))

Linear Regression

A single regression line through all data.

(-> data/iris
    (sk/lay-point :sepal_length :sepal_width)
    sk/lay-lm)

Per-Group Regression

Fit a regression line per group.

(-> data/iris
    (sk/view :petal_length :petal_width {:color :species})
    sk/lay-point
    sk/lay-lm)

Regression with Confidence Ribbon

Pass {:se true} to show a 95% confidence band around the line.

(-> data/iris
    (sk/view :sepal_length :sepal_width {:color :species})
    sk/lay-point
    (sk/lay-lm {:se true}))

Tips with Regression

Do smokers and non-smokers tip differently?

(-> data/tips
    (sk/view :total_bill :tip {:color :smoker})
    sk/lay-point
    sk/lay-lm)

LOESS Smoothing

A smooth curve through noisy data.

(def noisy-wave (let [r (rng/rng :jdk 42)]
                  {:x (range 50)
                   :y (map #(+ (Math/sin (* % 0.2)) (* 0.3 (- (rng/drandom r) 0.5)))
                           (range 50))}))

(-> noisy-wave
    (sk/lay-point :x :y)
    sk/lay-loess)

Heatmap (Auto-Binned)

Bin x and y into a grid, count points per cell.

(-> data/iris
    (sk/lay-tile :sepal_length :sepal_width))

Heatmap (Pre-Computed)

Use a numeric column for tile color.

(def grid-data
  (let [r (rng/rng :jdk 99)]
    {:x (for [i (range 5) _j (range 5)] i)
     :y (for [_i (range 5) j (range 5)] j)
     :value (repeatedly 25 #(rng/irandom r 100))}))

(-> grid-data
    (sk/lay-tile :x :y {:fill :value}))

Density 2D

KDE-smoothed 2D density heatmap.

(-> data/iris
    (sk/lay-density2d :sepal_length :sepal_width))

Density 2D with Points

Overlay scatter points on the density heatmap.

(-> data/iris
    (sk/lay-density2d :sepal_length :sepal_width)
    (sk/lay-point {:alpha 0.5}))

Contour Lines

Iso-density contour lines from 2D KDE.

(-> data/iris
    (sk/lay-contour :sepal_length :sepal_width))

Contour with Points

Contour lines overlaid on scatter points.

(-> data/iris
    (sk/lay-point :sepal_length :sepal_width {:alpha 0.3})
    (sk/lay-contour {:levels 8}))

What’s Next

• Polar — radial charts and pie-style visualizations
• Faceting — split any chart into panels by category

source: notebooks/napkinsketch_book/relationships.clj