R function to build a local URL for RMarkdown

localurl.R

library(tidyverse)

localurl <- function(document, path = ""){
  
  path     <- str_remove_all(path, "/$|^/")
  document <- str_remove_all(document, "/$|^/")
  
  path     <- file.path(path, document) %>% 
    str_remove_all("/$|^/")
  document <- last(str_split(path, pattern = "/", simplify = T))
  
  return(paste0("[", document, "](", path, ")"))
}

sample.Rmd

---
title: "Untitled"
author: "Martin"
date: "2 April 2019"
output: pdf_document
---

```{r setup, include=FALSE}
source(localurl.R)
```

We have evidence, see `r localurl("../data/evidence.pdf")`.

We also have more evidence here: `r localurl("moreevidence.pdf", "../data/")`