在RMarkdown中包含来自外部源R的功能

Question

Suppose I have a functions.R script in which I have defined a few functions:

foo <- function(x) print(x-2)
bar <- function(x) print(x^3)
...

Now I want to include only foo (and not the whole functions.R in a chunk in RMarkdown.

If I wanted all functions to be included, following this answer , I could have done this via:

``` {r, code = readLines("functions.R")}
```

However, I only need foo in the chunk. How can I do it? Thanks in advance.

Answer 1

I adapt the approach from this answer to a related question to solve this problem. ¹

I stored in the file functions.R your two example functions above:

foo <- function(x) print(x-2)
bar <- function(x) print(x^3)

I then create the following R Markdown document:

---
title: "SO Answer"
author: "duckmayr"
date: "7/8/2019"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

We set up a function to source an R script, but only assign to the global environment the functions we want:

```{r source_function}
source_functions <- function(fcn_names, file_name) {
    env <- new.env()
    source(file_name, local = env)
    for ( i in 1:length(fcn_names) ) {
        assign(fcn_names[i], get(fcn_names[i], envir = env), envir = .GlobalEnv)
    }
}
```

Then we can call it to get *only* the function `foo()`:

```{r get_foo}
source_functions("foo", "functions.R")
ls()
```

This will also work for multiple functions:

```{r get_foo_and_bar}
source_functions(c("foo", "bar"), "functions.R")
ls()
```

Which renders as:

We see that in the first call to source_functions() , only the foo() function is added to the global environment, but not the bar() function, which should work to solve your problem. If you wanted multiple functions from functions.R , this will also work as well, as demonstrated in the second call to source_functions() .

Update: Showing the Functions' Code

We can edit our source_functions() function to show the code of the functions it sources, like so:

source_functions <- function(fcn_names, file_name) {
    env <- new.env()
    source(file_name, local = env)
    n <- length(fcn_names)
    result <- character(n)
    for ( i in 1:n ) {
        name <- fcn_names[i]
        fcn <- get(name, envir = env)
        code <- capture.output(show(fcn))
        code <- paste(code[-which(grepl("<env", code))], collapse = " ")
        assign(name, fcn, envir = .GlobalEnv)
        result[i] <- paste(name, "<-", code, collapse = " ")
    }
    return(result)
}

Then our document renders as

---

1 _{That question and answer (1) was not in the context of R Markdown, and more importantly (2) only demonstrated how to get all functions from an R script (without getting other objects) rather than particular functions.}