Expand and Knit a Child Template Once per Row of a Parameter Grid

The loop that recurs in reports with one section per feature: [knitr::knit_expand()] the child template for each row, join the pieces and [knitr::knit_child()] them. Use it in a chunk with `results = "asis"`.

Usage

expand_child_template(
  template_path,
  param_grid,
  quiet = TRUE,
  sep = "\n\n",
  delim = c("{{", "}}"),
  expand_only = FALSE,
  envir = parent.frame()
)

Arguments

template_path

Path of the child template.

param_grid

A data frame (or named list of equal-length vectors), one row per child.

quiet

Passed to [knitr::knit_child()] (default `TRUE`).

sep

Text between the expanded children (default a blank line).

delim

Template markers for [knitr::knit_expand()] (default `c("", "")`).

expand_only

Return the expanded text without knitting it (default `FALSE`).

envir

Environment to knit in (default: the caller's).

Value

The knitted text, as `knitr::knit_child()` returns it (print it with `cat()`, or return it from a chunk with `results = "asis"`). With `expand_only = TRUE`, the expanded text.

Details

Each column of `param_grid` is a template variable: `feature` in the child is replaced by the value in column `feature` (change the markers with `delim`). The rows are expanded in order.

Examples

tmp <- tempfile(fileext = ".qmd")
writeLines("## {{label}}\n\nFeature `{{feature}}`.\n", tmp)
grid <- data.frame(feature = c("age", "bmi"), label = c("Age", "BMI"))
cat(expand_child_template(tmp, grid, expand_only = TRUE))
#> ## Age
#> 
#> Feature `age`.
#> 
#> 
#> ## BMI
#> 
#> Feature `bmi`.