Add pdf_combine.R file with pdf_combine function.

DESCRIPTION

@@ -1,13 +1,14 @@
 Package: staplr
 Type: Package
 Title: A Toolkit for PDF Files
-Version: 3.1.1
+Version: 3.2.0
 Depends: R (>= 3.4.0)
 Authors@R: c(
     person("Priyanga Dilini", "Talagala", email="pritalagala@gmail.com", role= c("aut","cre")),
     person("Ogan", "Mancarci", email="ogan.mancarci@gmail.com", role='aut'),
     person("Daniel", "Padfield", email= "d.padfield@exeter.ac.uk", role ='aut'),
-    person("Granville", "Matheson", email= "mathesong@gmail.com", role ='aut')
+    person("Granville", "Matheson", email= "mathesong@gmail.com", role ='aut'),
+    person("Pedro Rafael", "D. Marinho", email= "pedro.rafael.marinho@gmail.com", role ='ctb', comment = c(ORCID = "0000-0003-1591-8300"))
     )
 Description: Provides function to manipulate PDF files: 
     fill out PDF forms;
@@ -30,10 +31,12 @@ Imports:
   assertthat,
   glue,
   XML,
-  rJava
+  rJava,
+  fs,
+  purrr,
+  pdftools
 Suggests: 
   lattice,
-  testthat,
-  pdftools
+  testthat
 Encoding: UTF-8
 BugReports: https://github.com/pridiltal/staplr/issues

NAMESPACE

@@ -1,5 +1,6 @@
 # Generated by roxygen2: do not edit by hand
 
+export(combine_pdf)
 export(get_fields)
 export(idenfity_form_fields)
 export(remove_pages)
@@ -13,5 +14,17 @@ export(split_pdf)
 export(staple_pdf)
 import(utils)
 importFrom(assertthat,assert_that)
+importFrom(fs,file_temp)
+importFrom(fs,file_temp_push)
+importFrom(fs,path_ext_remove)
+importFrom(fs,path_file)
+importFrom(glue,glue)
+importFrom(pdftools,pdf_combine)
+importFrom(pdftools,pdf_length)
+importFrom(pdftools,pdf_subset)
+importFrom(purrr,flatten_dbl)
+importFrom(purrr,map2_dbl)
+importFrom(purrr,map_if)
+importFrom(purrr,walk2)
 importFrom(stringr,str_extract)
 importFrom(tcltk,tk_choose.dir)

R/combine_pdf.R

@@ -0,0 +1,82 @@
+#' Combine multiple PDF files
+#' @description Combine multiple PDF files by delimiting the sequences of pages in each file.
+#' @importFrom glue glue
+#' @importFrom pdftools pdf_subset pdf_combine pdf_length
+#' @importFrom purrr map2_dbl walk2 flatten_dbl map_if
+#' @importFrom fs file_temp file_temp_push path_ext_remove path_file
+#' @param vec_input Vector with paths of PDF files to be combined.
+#' @param output PDF file path result of the combination.
+#' @param start_pages Vector with the initial pages of each file. If \code{NA},
+#' the default, will be considered the first page.
+#' @param end_pages Vector with the final pages of each file. If \code{NA}, the
+#' default, will be considered the last page.
+#' @return
+#' In the path informed in \code{output}, the PDF file resulting from the combination
+#' of multiple files passed to \code{vec_output} will be saved.
+#' @export
+#' @examples
+#'
+#' \dontrun{
+#' combine_pdf(
+#'    vec_input =
+#'       c(
+#'         "file_1.pdf",
+#'         "file_2.pdf",
+#'       ),
+#'    output = "output.pdf",
+#'    start_pages = c(NA, NA),
+#'    end_pages = c(NA, NA)
+#'  )
+#' }
+
+combine_pdf <- function(vec_input, output = "output.pdf", start_pages = NA, end_pages = NA) {
+
+  if(length(start_pages) != length(vec_input) || length(end_pages) != length(vec_input))
+    stop("Start_pages and end_pages must be a vector of the same length as vec_input!")
+
+  start_pages <-
+    flatten_dbl(
+      map_if(
+        .x = start_pages,
+        .f = function(x) 1,
+        .p = is.na
+      )
+    )
+
+  f <- function(x, y)
+    ifelse(
+      is.na(x),
+      pdf_length(vec_input[y]),
+      x
+    )
+
+  end_pages <-
+    purrr::map2_dbl(
+      .x = end_pages,
+      .y = seq_along(vec_input),
+      .f = f
+    )
+
+  files <-
+    file_temp_push(
+      glue(
+        "{tempdir()}/{path_ext_remove(path_file(output))}_{1L:length(vec_input)}.pdf"
+      )
+    )
+
+  one_step <- function(x, y) {
+    pdf_subset(
+        input = x,
+        output = file_temp(),
+        pages = start_pages[y]:end_pages[y]
+      )
+  }
+
+  walk2(
+    .x = vec_input,
+    .y = 1L:length(vec_input),
+    .f = ~ one_step(.x, .y)
+  )
+
+  pdf_combine(input = files, output = output)
+}