You can use inline R code (see Section 3.1) anywhere in an Rmd document, including the YAML metadata section. This means some YAML metadata can be dynamically generated with inline R code, such as the document title. For example:

    1. ---
    2. title: "An analysis of `r nrow(mtcars)` cars"
    3. ---

    If your title depends on an R variable created later in the document, you may add the title field in a later YAML section, e.g., the following:

    1. ---
    2. author: "Smart Analyst"
    3. output: pdf_document
    4. ---
    6. I just tried really hard to calculate our market share:
    8. ```{r}
    9. share <- runif(1)
    10. ```
    12. ---
    13. title: "Our market share is `r round(100 * share, 2)`% now!"
    14. ---
    16. I feel `r if(share > 0.8) "happy" else "sad"` about it.

    In the example above, we added the document title after we created the variable share. The title works in this case because Pandoc can read any number of YAML sections in a document (and merge them).

    You can also generate titles or any YAML fields dynamically from parameters in parameterized reports (see Section 17.4), e.g.,

    1. ---
    2. title: "`r params$doc_title`"
    3. author: "Smart Analyst"
    4. params:
    5.   doc_title: "The Default Title"
    6. ---

    With the title being a dynamic parameter, you can easily generate a batch of reports with different titles.

    We used the title as the example in this section, but the idea can be applied to any metadata fields in the YAML section.