Linear line

Layers are declared with the DRAW clause. Read the documentation for this clause for a thorough description of how to use it.

The linear layer is used to draw diagonal reference lines based on a coefficient and intercept. This is useful for adding regression lines, diagonal guides, or mathematical functions to plots. The lines extend across the full extent of the x-axis, regardless of the data range. The layer is named for the following formula:

\[ y = a + \beta x \]

Where \(a\) is the intercept and \(\beta\) is the coef.

Aesthetics

The following aesthetics are recognised by the abline layer.

Required

• coef: The coefficient/slope of the line i.e. the amount \(y\) increases for every unit of \(x\).
• intercept: The intercept where the line crosses the y-axis at \(x = 0\).

Optional

• colour/stroke: The colour of the line
• opacity: The opacity of the line
• linewidth: The width of the line
• linetype: The type of the line, i.e. the dashing pattern

Settings

The linear layer has no additional settings.

Data transformation

The linear layer does not transform its data but passes it through unchanged.

Examples

Add a simple reference line to a scatterplot:

VISUALISE FROM ggsql:penguins
  DRAW point MAPPING bill_len AS x, bill_dep AS y
  DRAW linear MAPPING 0.4 AS coef, -1 AS intercept

Add multiple reference lines with different colors from a separate dataset:

WITH lines AS (
    SELECT * FROM (VALUES
        (0.4, -1, 'Line A'),
        (0.2, 8, 'Line B'),
        (0.8, -19, 'Line C')
    ) AS t(coef, intercept, label)
)
VISUALISE FROM ggsql:penguins
  DRAW point MAPPING bill_len AS x, bill_dep AS y
  DRAW linear
    MAPPING 
      coef AS coef, 
      intercept AS intercept, 
      label AS colour
    FROM lines