Add ties.method="last" to frank

NEWS.md

@@ -73,6 +73,8 @@ unit = "s")
 
 10. The dimensions of objects in a `list` column are now displayed, [#3671](https:/Rdatatable/data.table/issues/3671). Thanks to @randomgambit for the request, and Tyson Barrett for the PR.
 
+11. `frank` gains `ties.method='last'`, paralleling the same in `base::order` which has been available since R 3.3.0 (April 2016), [#1689](https:/Rdatatable/data.table/issues/1689). Thanks @abudis for the encouragement to accommodate this.
+
 ## BUG FIXES
 
 1. A NULL timezone on POSIXct was interpreted by `as.IDate` and `as.ITime` as UTC rather than the session's default timezone (`tz=""`) , [#4085](https:/Rdatatable/data.table/issues/4085).

R/frank.R

@@ -1,4 +1,4 @@
-frankv = function(x, cols=seq_along(x), order=1L, na.last=TRUE, ties.method=c("average", "first", "random", "max", "min", "dense")) {
+frankv = function(x, cols=seq_along(x), order=1L, na.last=TRUE, ties.method=c("average", "first", "last", "random", "max", "min", "dense")) {
  ties.method = match.arg(ties.method)
  if (!length(na.last)) stop('length(na.last) = 0')
  if (length(na.last) != 1L) {
@@ -48,7 +48,7 @@ frankv = function(x, cols=seq_along(x), order=1L, na.last=TRUE, ties.method=c("a
  xorder = seq_along(x[[1L]])
  }
  ans = switch(ties.method,
- average = , min = , max =, dense = {
+ average = , min = , max =, dense =, last = {
  rank = .Call(Cfrank, xorder, xstart, uniqlengths(xstart, length(xorder)), ties.method)
  },
  first = , random = {
@@ -65,7 +65,7 @@ frankv = function(x, cols=seq_along(x), order=1L, na.last=TRUE, ties.method=c("a
  ans
 }
 
-frank = function(x, ..., na.last=TRUE, ties.method=c("average", "first", "random", "max", "min", "dense")) {
+frank = function(x, ..., na.last=TRUE, ties.method=c("average", "first", "last", "random", "max", "min", "dense")) {
  cols = substitute(list(...))[-1L]
  if (identical(as.character(cols), "NULL")) {
  cols = NULL

inst/tests/tests.Rraw

@@ -5480,7 +5480,7 @@ test_no = 1368.0
 for (i in seq_along(dt)) {
  col = dt[[i]]
  for (j in list(TRUE, FALSE, "keep")) {
- for (k in c("average", "min", "max", "first")) {
+ for (k in c("average", "min", "max", "first", "last")) {
  if (k == "random") set.seed(45L)
  if (class(col) == "integer64") {
  r1 = rank(as.integer(col), ties.method=k, na.last=j)
@@ -5511,7 +5511,7 @@ if (test_bit64) dt[, DD := as.integer64(DD)]
 test_no = 1369.0
 for (i in seq_along(dt)) {
  col = dt[[i]]
- for (k in c("average", "min", "max", "first")) {
+ for (k in c("average", "min", "max", "first", "last")) {
  if (k == "random") set.seed(45L)
  if (class(col) == "integer64") {
  r1 = rank(as.integer(col), ties.method=k, na.last=NA)

man/frank.Rd

@@ -4,19 +4,19 @@
 \alias{rank}
 \title{Fast rank}
 \description{
- Similar to \code{base::rank} but \emph{much faster}. And it accepts vectors, lists, data.frames or data.tables as input. In addition to the \code{ties.method} possibilities provided by \code{base::rank}, it also provides \code{ties.method="dense"}.
- 
+ Similar to \code{base::rank} but \emph{much faster}. And it accepts vectors, lists, \code{data.frame}s or \code{data.table}s as input. In addition to the \code{ties.method} possibilities provided by \code{base::rank}, it also provides \code{ties.method="dense"}.
+
  Like \code{\link{forder}}, sorting is done in "C-locale"; in particular, this may affect how capital/lowercase letters are ranked. See Details on \code{forder} for more.
 
  \code{bit64::integer64} type is also supported.
 }
 
 \usage{
 frank(x, \dots, na.last=TRUE, ties.method=c("average",
- "first", "random", "max", "min", "dense"))
+ "first", "last", "random", "max", "min", "dense"))
 
 frankv(x, cols=seq_along(x), order=1L, na.last=TRUE,
- ties.method=c("average", "first", "random",
+ ties.method=c("average", "first", "last", "random",
  "max", "min", "dense"))
 
 }
@@ -33,7 +33,7 @@ frankv(x, cols=seq_along(x), order=1L, na.last=TRUE,
 
  \code{frank} is not limited to vectors. It accepts \code{data.table}s (and \code{list}s and \code{data.frame}s) as well. It accepts unquoted column names (with names preceded with a \code{-} sign for descending order, even on character vectors), for e.g., \code{frank(DT, a, -b, c, ties.method="first")} where \code{a,b,c} are columns in \code{DT}. The equivalent in \code{frankv} is the \code{order} argument.
 
- In addition to the \code{ties.method} values possible using base's \code{\link[base]{rank}}, it also provides another additional argument \emph{"dense"} which returns the ranks without any gaps in the ranking. See examples.
+ In addition to the \code{ties.method} values possible using base's \code{\link[base]{rank}}, it also provides another additional argument \code{"dense"} which returns the ranks without any gaps in the ranking. See examples.
 }
 \value{
  A numeric vector of length equal to \code{NROW(x)} (unless \code{na.last = NA}, when missing values are removed). The vector is of integer type unless \code{ties.method = "average"} when it is of double type (irrespective of ties).

src/frank.c

@@ -69,14 +69,16 @@ SEXP dt_na(SEXP x, SEXP cols) {
 
 SEXP frank(SEXP xorderArg, SEXP xstartArg, SEXP xlenArg, SEXP ties_method) {
  const int *xstart = INTEGER(xstartArg), *xlen = INTEGER(xlenArg), *xorder = INTEGER(xorderArg);
- enum {MEAN, MAX, MIN, DENSE, SEQUENCE} ties = MEAN; // RUNLENGTH
+ enum {MEAN, MAX, MIN, DENSE, SEQUENCE, LAST} ties; // RUNLENGTH
 
- if (!strcmp(CHAR(STRING_ELT(ties_method, 0)), "average")) ties = MEAN;
- else if (!strcmp(CHAR(STRING_ELT(ties_method, 0)), "max")) ties = MAX;
- else if (!strcmp(CHAR(STRING_ELT(ties_method, 0)), "min")) ties = MIN;
- else if (!strcmp(CHAR(STRING_ELT(ties_method, 0)), "dense")) ties = DENSE;
- else if (!strcmp(CHAR(STRING_ELT(ties_method, 0)), "sequence")) ties = SEQUENCE;
- // else if (!strcmp(CHAR(STRING_ELT(ties_method, 0)), "runlength")) ties = RUNLENGTH;
+ const char *pties = CHAR(STRING_ELT(ties_method, 0));
+ if (!strcmp(pties, "average")) ties = MEAN;
+ else if (!strcmp(pties, "max")) ties = MAX;
+ else if (!strcmp(pties, "min")) ties = MIN;
+ else if (!strcmp(pties, "dense")) ties = DENSE;
+ else if (!strcmp(pties, "sequence")) ties = SEQUENCE;
+ else if (!strcmp(pties, "last")) ties = LAST;
+ // else if (!strcmp(pties, "runlength")) ties = RUNLENGTH;
  else error(_("Internal error: invalid ties.method for frankv(), should have been caught before. please report to data.table issue tracker")); // # nocov
  const int n = length(xorderArg);
  SEXP ans = PROTECT(allocVector(ties==MEAN ? REALSXP : INTSXP, n));
@@ -118,6 +120,15 @@ SEXP frank(SEXP xorderArg, SEXP xstartArg, SEXP xlenArg, SEXP ties_method) {
  ians[xorder[j]-1] = k++;
  }
  break;
+ case LAST :
+ for (int i=0; i<length(xstartArg); ++i) {
+ // alternatively, also loop k from xstart[i]+xlen[i]-1 and decrement
+ int offset = 2*xstart[i]+xlen[i]-2;
+ for (int j=xstart[i]-1; j<xstart[i]+xlen[i]-1; ++j) {
+ ians[xorder[j]-1] = offset-j;
+ }
+ }
+ break;
  // case RUNLENGTH :
  // for (i = 0; i < length(xstartArg); i++) {
  // k=1;