Extract package names from R scripts

Question

I am trying to write a function to extract package names from a list of R script files. My regular expression do not seem to be working and I am not sure why. For begginers, I am not able to match lines that include library . For example

str <- c("           library(abc)", "library(def)", "some other text")
grep("library\\(", str, value = TRUE)
grep("library\\(+[A-z]\\)", str, value = TRUE)

Why does my second grep do not return elements 1 and 2 from the str vector? I have tried so many options but all my results come back empty.

Answer 1

Your second grep does not return 1,2 for two reasons.

1. You used value=TRUE which makes it return the matching string instead of the location. and
2. You misplaced the +. You want grep("library\\\\(\\\\w+\\\\)", str)

Answer 2

If you'd like something a bit more robust that will handle some edge cases ( library() takes a number of parameters and the package one can be a name/symbol or a string and doesn't necessarily have to be specified first):

library(purrr)

script <-  '
library(js) ; library(foo)
#
library("V8")
ls()
library(package=rvest)
TRUE
library(package="hrbrthemes")
1 + 1
library(quietly=TRUE, "ggplot2")
library(quietly=TRUE, package=dplyr, verbose=TRUE)
'
x <- parse(textConnection(script)) # parse w/o eval

keep(x, is.language) %>%                       # `library()` is a language object
  keep(~languageEl(.x, 1) == "library") %>%    # other things are too, so only keep `library()` ones
  map(as.call) %>%                             # turn it into a `call` object 
  map(match.call, definition = library) %>%    # so we can match up parameters and get them in the right order
  map(languageEl, 2) %>%                       # language element 1 is `library`
  map_chr(as.character) %>%                    # turn names/symbols into characters
  sort()                                       # why not
## [1] "dplyr"      "foo"        "ggplot2"    "hrbrthemes" "js"         "rvest"      "V8"

This won't catch library() calls within functions (it could be expanded to do that) but if top-level edge cases are infrequent, there is an even smaller likelihood of ones in functions (those wld likely use require() as well).