10. Parameterized Reports

So far, we have created our report only for Adelie penguins. But what if we want the same report for all three penguin species? Instead of maintaining three separate documents, we can use parameters: A template that is filled with different values when rendering.

The concept

A parameterized report is like a form with blanks:

1. The template defines parameters with default values
2. When rendering, other values can be passed
3. The report adapts automatically

Defining parameters

Parameters are defined in the YAML header under params::

---
title: "Penguin Report"
format: docx
params:
  species: "Adelie"
---

Here, species is the parameter name and "Adelie" is the default value.

Using parameters in code

In R code, you access parameters with params$parametername:

# Filter data based on parameter
selected_penguins <- penguins %>%
  filter(species == params$species) %>%
  drop_na()

The body text can also contain parameters:

This report analyzes **Adelie** penguins.

A complete example

Here is our penguin report as a parameterized version:

---
title: "Penguin Report"
subtitle: "Adelie Penguins"
author: "Research Team"
date: today
format: docx
params:
  species: "Adelie"
execute:
  echo: false
  warning: false
  message: false
---

# Introduction

This report analyzes **Adelie** penguins from the
Palmer Penguins dataset. The dataset includes 146
individuals of this species.

# Descriptive Statistics

```{r}
#| label: tbl-params-summary
#| tbl-cap: "Summary of measurements"
selected_penguins %>%
  summarise(
    N = n(),
    `Bill Length (mm)` = round(mean(bill_length_mm), 1),
    `Body Mass (g)` = round(mean(body_mass_g), 0)
  ) %>%
  flextable() %>%
  autofit()
```

# Visualization

```{r}
#| label: fig-params-scatter
#| fig-cap: "Bill measurements of the selected penguin species"
#| fig-width: 5
#| fig-height: 4
ggplot(selected_penguins, aes(x = bill_length_mm, y = bill_depth_mm)) +
  geom_point(alpha = 0.6) +
  labs(
    x = "Bill Length (mm)",
    y = "Bill Depth (mm)",
    title = glue::glue("{params$species} Penguins")
  ) +
  theme_minimal()
```

Rendering with different parameters

In RStudio

1. Click on the arrow next to the Render button
2. Select “Render with Parameters…”
3. A dialog opens where you can change the values

Via command line

quarto render report.qmd -P species:Gentoo

Multiple parameters:

quarto render report.qmd -P species:Chinstrap -P year:2008

Programmatically in R

# Render one report
quarto::quarto_render(
  input = "report.qmd",
  execute_params = list(species = "Gentoo"),
  output_file = "report_gentoo.docx"
)

Rendering all variants at once

With a loop, you can automatically generate all versions:

library(purrr)

# All penguin species
species_list <- c("Adelie", "Chinstrap", "Gentoo")

# Render a report for each species
walk(species_list, function(sp) {
  quarto::quarto_render(
    input = "report.qmd",
    execute_params = list(species = sp),
    output_file = glue::glue("report_{tolower(sp)}.docx")
  )
})

This creates three files: report_adelie.docx, report_chinstrap.docx, report_gentoo.docx.

Multiple parameters

You can define any number of parameters:

params:
  species: "Adelie"
  island: "Biscoe"
  min_year: 2007
  include_plots: true

And in code:

filtered_data <- penguins %>%
  filter(
    species == params$species,
    island == params$island,
    year >= params$min_year
  )

# Conditional execution
if (params$include_plots) {
  # Plot code here
}

Parameter types

Parameters can have different types:

params:
  species: "Adelie"           # Text
  sample_size: 100            # Number
  include_plots: true         # Boolean
  islands:                    # List
    - Biscoe
    - Dream

Dynamic titles

The title can contain parameters:

---
title: "Adelie Penguin Analysis"
params:
  species: "Adelie"
---

Or simpler in the subtitle:

---
title: "Penguin Analysis"
subtitle: "Adelie"
params:
  species: "Adelie"
---

Practical use cases

Application	Parameters
Reports per region	region, year
Client reports	client_name, client_id
Test versions	include_draft_watermark: true
Language versions	language: "de"
Data sources	data_file: "data_2024.csv"

Tips

Set sensible defaults

The default value should be a typical, working value — this way you can easily test the template.

Validate parameter values

At the beginning of the document, check if the parameters are valid:

# Check if species exists
valid_species <- c("Adelie", "Chinstrap", "Gentoo")

if (!params$species %in% valid_species) {
  stop(glue::glue(
    "Invalid species: {params$species}. ",
    "Allowed are: {paste(valid_species, collapse = ', ')}"
  ))
}

Output file names

When mass-producing, use meaningful file names:

output_file = glue::glue(
  "report_{params$species}_{Sys.Date()}.docx"
)

TipExercise: Create a parameterized report

1. Take the previous penguin report
2. Add a species parameter with default value “Adelie”
3. Replace all places that refer to Adelie with params$species
4. Render the report with different species (Adelie, Chinstrap, Gentoo)
5. Bonus: Write a loop that automatically generates all three reports

Further resources

• Quarto Parameters — Official documentation
• Parameterized Reporting with Quarto — Rendering options

What is next

In the final chapter, we will look beyond Word: PDF export with Typst, presentations with Reveal.js, and HTML documents — all with the same Quarto knowledge.