make_category_svc: Set up spatially varying coefficients for category...

In sdmTMB: Spatial and Spatiotemporal SPDE-Based GLMMs with 'TMB'

Set up spatially varying coefficients for category composition models

Description

This function helps set up the data structure, formula, and mapping needed for fitting spatially varying coefficient models with categories (e.g., ages, length bins, species) that have both spatial and spatiotemporal random fields. It's particularly useful for age or length composition standardization models.

Usage

make_category_svc(
  data,
  category_column,
  time_column,
  share_spatial_sd = TRUE,
  share_spatiotemporal_sd = TRUE
)

Arguments

data	Data frame containing the composition data.
category_column	Character. Name of the category column (e.g., "Age", "length_bin", "species").
time_column	Character. Name of the time column (e.g., "Year").
share_spatial_sd	Logical. If TRUE, all categories share the same spatial SD. If FALSE, each category gets its own spatial SD.
share_spatiotemporal_sd	Logical. If TRUE, all category-time combinations share the same spatiotemporal SD. If FALSE, each gets its own.

Details

This function creates spatially varying coefficient structures for composition models by setting up:

1. Spatial fields: One field per category (e.g., age-specific spatial fields) 2. Spatiotemporal fields: One field per category-time combination (e.g., age-year fields)

The sharing of variance parameters is controlled by share_spatial_sd and share_spatiotemporal_sd. When TRUE, all fields of that type share the same variance parameter, which is more parsimonious but assumes similar variance magnitudes across categories.

The resulting model structure allows each category to have its own spatial pattern and temporal variation while controlling parameter sharing for identifiability and computational efficiency.

Value

A list containing:

• data_expanded: Data frame with added model matrix columns for use in sdmTMB().

• svc_formula: Formula for the spatial_varying argument in sdmTMB().

• svc_map: Map list for the map argument in sdmTMBcontrol().

• info: List with summary information about the model structure.

Examples

set.seed(123)
data <- data.frame(
  age = factor(rep(1:3, each = 20)),
  year = rep(2020:2022, 20),
  abundance = rnorm(60),
  x = runif(60), y = runif(60)
)

# Set up model components
setup <- make_category_svc(
  data = data,
  category_column = "age",
  time_column = "year",
  share_spatial_sd = TRUE,
  share_spatiotemporal_sd = TRUE
)

# Check the setup
setup$info

# See the age composition standardization vignette for more details

sdmTMB documentation built on Nov. 26, 2025, 9:06 a.m.