difference_smooths {gratia}

Differences of factor smooth interactions

Description

Estimates pairwise differences (comparisons) between factor smooth interactions (smooths with a factor by argument) for pairs of groups defined by the factor. The group means can be optionally included in the difference.

Usage

difference_smooths(model, ...)

## S3 method for class 'gam'
difference_smooths(
  model,
  select = NULL,
  smooth = deprecated(),
  n = 100,
  ci_level = 0.95,
  data = NULL,
  group_means = FALSE,
  partial_match = TRUE,
  unconditional = FALSE,
  frequentist = FALSE,
  ...
)

Arguments

model

A fitted model.

...

arguments passed to other methods. Not currently used.

select

character, logical, or numeric; which smooths to plot. If NULL, the default, then all model smooths are drawn. Numeric select indexes the smooths in the order they are specified in the formula and stored in object. Character select matches the labels for smooths as shown for example in the output from summary(object). Logical select operates as per numeric select in the order that smooths are stored.

smooth

Use select instead.

n

numeric; the number of points at which to evaluate the difference between pairs of smooths.

ci_level

numeric between 0 and 1; the coverage of credible interval.

data

data frame of locations at which to evaluate the difference between smooths.

group_means

logical; should the group means be included in the difference?

partial_match

logical; should smooth match partially against smooths? If partial_match = TRUE, smooth must only be a single string, a character vector of length 1. Unlike similar functions, the default here is TRUE because the intention is that users will be matching against factor-by smooth labels.

unconditional

logical; account for smoothness selection in the model?

frequentist

logical; use the frequentist covariance matrix?

Examples

load_mgcv()

df <- data_sim("eg4", seed = 42)
m <- gam(y ~ fac + s(x2, by = fac) + s(x0), data = df, method = "REML")

sm_dif <- difference_smooths(m, select = "s(x2)")
sm_dif

draw(sm_dif)

# include the groups means for `fac` in the difference
sm_dif2 <- difference_smooths(m, select = "s(x2)", group_means = TRUE)
draw(sm_dif2)