[GitHub] [arrow] pachadotdev commented on a change in pull request #10624: ARROW-12992: [R] bindings for substr(), substring(), str_sub()

[GitBox <gi...@apache.org>]

pachadotdev commented on a change in pull request #10624:
URL: https://github.com/apache/arrow/pull/10624#discussion_r664559978



##########
File path: r/R/dplyr-functions.R
##########
@@ -280,6 +280,45 @@ nse_funcs$str_trim <- function(string, side = c("both", "left", "right")) {
   Expression$create(trim_fun, string)
 }
 
+nse_funcs$substr <- function(string, start, stop) {
+  assert_that(
+    length(start) == 1,
+    msg = "Start of length != 1 not supported in Arrow"
+  )
+  assert_that(
+    length(end) == 1,
+    msg = "End of length != 1 not supported in Arrow"
+  )
+
+  if (start > stop) {
+    start <- 0
+    stop <- 0
+  } else {
+    start <- max(0, start - 1)
+    stop <- max(0, stop)
+    start_stop <- c(min(start, stop), max(start, stop))
+    start <- start_stop[1]
+    stop <- start_stop[2]
+  }

Review comment:
       it's more a verification than a formal requirement




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