Parameters
Overview
You may have a set of parameters that are used to create different variations of a document. For example:
- Showing results for a specific geographic location.
- Running a report that covers a specific time period.
- Running a single analysis multiple times for different assumptions.
This article describes how to define and use computational parameters with Quarto.
Definition
Adding parameter definitions to a document works differently depending on whether you are using the Jupyter or Knitr engine.
Jupyter
For Jupyter, Quarto uses the same syntax for defining parameters as Papermill. To parameterize a document, designate a cell with the tag parameters and provide appropriate default values:
```{python}
#| tags: [parameters]
alpha = 0.1
ratio = 0.1
```The parameters are available in the top level environment:
```{python}
alpha
```When the document is executed with a set of new parameters a cell is injected which overrides these defaults as appropriate.
Knitr
For Knitr, the standard Knitr params YAML option is used to define parameters. For example:
---
params:
alpha: 0.1
ratio: 0.1
---The parameters are available in the params list:
```{r}
params$alpha
```Rendering
To render using different parameters you can pass them on the command line using the -P flag (this works for both .ipynb or .qmd files):
Terminal
quarto render document.ipynb -P alpha:0.2 -P ratio:0.3Alternatively you can create a YAML file that defines the parameter values you want to render with, then call quarto render with the --execute-params flag:
Terminal
quarto render document.qmd --execute-params params.yml