New xml_find_int() to get integers from an XPath (#412)

NAMESPACE

@@ -80,6 +80,9 @@ S3method(xml_find_chr,xml_nodeset)
 S3method(xml_find_first,xml_missing)
 S3method(xml_find_first,xml_node)
 S3method(xml_find_first,xml_nodeset)
+S3method(xml_find_int,xml_missing)
+S3method(xml_find_int,xml_node)
+S3method(xml_find_int,xml_nodeset)
 S3method(xml_find_lgl,xml_missing)
 S3method(xml_find_lgl,xml_node)
 S3method(xml_find_lgl,xml_nodeset)
@@ -149,6 +152,7 @@ export(xml_dtd)
 export(xml_find_all)
 export(xml_find_chr)
 export(xml_find_first)
+export(xml_find_int)
 export(xml_find_lgl)
 export(xml_find_num)
 export(xml_find_one)

NEWS.md

@@ -1,5 +1,8 @@
 # xml2 (development version)
 
+* `xml_find_int()` analogous to `xml_find_num()` for returning integers 
+  matched by an XPath (#365, @michaelchirico).
+
 * Now compatible with limxml2 2.12.0 and later (@KNnut).
 
 * Fix format string issues detected in R-devel.

R/xml_find.R

@@ -178,6 +178,33 @@ xml_find_num.xml_missing <- function(x, xpath, ns = xml_ns(x)) {
   numeric(0)
 }
 
+#' @export
+#' @rdname xml_find_all
+xml_find_int <- function(x, xpath, ns = xml_ns(x)) {
+  UseMethod("xml_find_int")
+}
+
+#' @export
+xml_find_int.xml_node <- function(x, xpath, ns = xml_ns(x)) {
+  res <- .Call(xpath_search, x$node, x$doc, xpath, ns, Inf)
+  check_number_whole(res, arg = I(paste0("Element at path `", xpath, "`")))
+  as.integer(res)
+}
+
+#' @export
+xml_find_int.xml_nodeset <- function(x, xpath, ns = xml_ns(x)) {
+  if (length(x) == 0) {
+    return(integer())
+  }
+
+  vapply(x, function(x) xml_find_int(x, xpath = xpath, ns = ns), integer(1))
+}
+
+#' @export
+xml_find_int.xml_missing <- function(x, xpath, ns = xml_ns(x)) {
+  integer(0)
+}
+
 #' @export
 #' @rdname xml_find_all
 xml_find_chr <- function(x, xpath, ns = xml_ns(x)) {

tests/testthat/_snaps/xml_find.md

@@ -2,6 +2,24 @@
 
     Element at path `//z` must be a number, not a <xml_missing> object.
 
+# xml_find_int errors with non integer results
+
+    Code
+      xml_find_int(x, "//z")
+    Condition
+      Error in `xml_find_int()`:
+      ! Element at path `//z` must be a whole number, not a <xml_missing> object.
+    Code
+      xml_find_int(x, "//y")
+    Condition
+      Error in `xml_find_int()`:
+      ! Element at path `//y` must be a whole number, not a list.
+    Code
+      xml_find_int(x, "number(1.1)")
+    Condition
+      Error in `xml_find_int()`:
+      ! Element at path `number(1.1)` must be a whole number, not the number 1.1.
+
 # xml_find_chr errors with non character results
 
     Element at path `//z` must be a single string, not a <xml_missing> object.

tests/testthat/test-xml_find.R

@@ -85,6 +85,24 @@ test_that("xml_find_num returns a numeric result", {
   expect_equal(xml_find_num(x, "1 div floor(-0)"), -Inf)
 })
 
+# Find int ---------------------------------------------------------------------
+test_that("xml_find_int errors with non integer results", {
+  x <- read_xml("<x><y/><y/></x>")
+  expect_snapshot(error = TRUE, {
+    xml_find_int(x, "//z")
+    xml_find_int(x, "//y")
+    xml_find_int(x, "number(1.1)")
+  })
+})
+
+test_that("xml_find_int returns a integer result", {
+  x <- read_xml("<x><y>1</y><y/></x>")
+
+  expect_identical(xml_find_int(x, "1 div floor(-0.1)"), -1L)
+  expect_identical(xml_find_int(x, "number(//y)"), 1L)
+  expect_identical(xml_find_int(x, "string-length(string('abcd'))"), 4L)
+})
+
 # Find chr ---------------------------------------------------------------------
 test_that("xml_find_chr errors with non character results", {
   x <- read_xml("<x><y/><y/></x>")