Faster uniqueN(v) for logical v

NEWS.md

@@ -65,10 +65,22 @@
 
 13. `unique(DT)` now returns `DT` early when there are no duplicates to save RAM, [#2013](https://github.com/Rdatatable/data.table/issues/2013). Thanks to Michael Chirico for the PR.
 
-14. Subsetting optimization with keys and indices is now possible for compound queries like `DT[a==1 & b==2]`, [#2472](https://github.com/Rdatatable/data.table/issues/2472).
+14. `uniqueN()` is now faster on logical vectors. Thanks to Hugh Parsonage for [PR#2648](https://github.com/Rdatatable/data.table/pull/2648).
+    ```
+    N = 1e9
+                                     was      now
+    x = c(TRUE,FALSE,NA,rep(TRUE,N))
+    uniqueN(x) == 3                 5.4s    0.00s
+    x = c(TRUE,rep(FALSE,N), NA)
+    uniqueN(x,na.rm=TRUE) == 2      5.4s    0.00s
+    x = c(rep(TRUE,N),FALSE,NA)
+    uniqueN(x) == 3                 6.7s    0.38s
+    ```
+
+15. Subsetting optimization with keys and indices is now possible for compound queries like `DT[a==1 & b==2]`, [#2472](https://github.com/Rdatatable/data.table/issues/2472).
 Thanks to @MichaelChirico for reporting and to @MarkusBonsch for the implementation.
 
-15. `melt.data.table` now offers friendlier functionality for providing `value.name` for `list` input to `measure.vars`, [#1547](https://github.com/Rdatatable/data.table/issues/1547). Thanks @MichaelChirico and @franknarf1 for the suggestion and use cases, @jangorecki and @mrdwab for implementation feedback, and @MichaelChirico for ultimate implementation.
+16. `melt.data.table` now offers friendlier functionality for providing `value.name` for `list` input to `measure.vars`, [#1547](https://github.com/Rdatatable/data.table/issues/1547). Thanks @MichaelChirico and @franknarf1 for the suggestion and use cases, @jangorecki and @mrdwab for implementation feedback, and @MichaelChirico for ultimate implementation.
 
 #### BUG FIXES
 

R/duplicated.R

@@ -142,7 +142,10 @@ uniqueN <- function(x, by = if (is.list(x)) seq_along(x) else NULL, na.rm=FALSE)
   if (is.null(x)) return(0L)
   if (!is.atomic(x) && !is.data.frame(x))
     stop("x must be an atomic vector or data.frames/data.tables")
-  if (is.atomic(x)) x = as_list(x)
+  if (is.atomic(x)) {
+    if (is.logical(x)) return(.Call(CuniqueNlogical, x, na.rm=na.rm))
+    x = as_list(x)
+  }
   if (is.null(by)) by = seq_along(x)
   o = forderv(x, by=by, retGrp=TRUE, na.last=if (!na.rm) FALSE else NA)
   starts = attr(o, 'starts')

inst/tests/tests.Rraw

@@ -6486,6 +6486,22 @@ DT <- data.table(A = rep(1:3, each=4), B = rep(1:4, each=3), C = rep(1:2, 6))
 test(1475.1, uniqueN(DT), 10L)
 test(1475.2, DT[, .(uN=uniqueN(.SD)), by=A], data.table(A=1:3, uN=c(3L,4L,3L)))
 
+# specialized uniqueN for logical vectors, PR#2648
+test(1475.3, uniqueN(c(NA, TRUE, FALSE)),                3L)
+test(1475.4, uniqueN(c(NA, TRUE, FALSE), na.rm = TRUE),  2L)
+test(1475.5, uniqueN(c(TRUE, FALSE), na.rm = TRUE),      2L)
+test(1475.6, uniqueN(c(TRUE, FALSE)),                    2L)
+test(1475.7, uniqueN(c(TRUE, NA)),                       2L)
+test(1475.8, uniqueN(c(TRUE, NA), na.rm=TRUE),           1L)
+test(1475.9, uniqueN(c(FALSE, NA)),                      2L)
+test(1475.11, uniqueN(c(FALSE, NA), na.rm=TRUE),         1L)
+test(1475.12, uniqueN(c(NA,NA)),                         1L)
+test(1475.13, uniqueN(c(NA,NA), na.rm=TRUE),             0L)
+test(1475.14, uniqueN(NA),                               1L)
+test(1475.15, uniqueN(NA, na.rm=TRUE),                   0L)
+test(1475.16, uniqueN(logical()),                        0L)
+test(1475.17, uniqueN(logical(), na.rm=TRUE),            0L)
+
 # preserve class attribute in GForce mean (and sum)
 DT <- data.table(x = rep(1:3, each = 3), y = as.Date(seq(Sys.Date(), (Sys.Date() + 8), by = "day")))
 test(1476.1, DT[, .(y=mean(y)), x], setDT(aggregate(y ~ x, DT, mean)))

src/data.table.h

@@ -4,6 +4,7 @@
 // #include <signal.h> // the debugging machinery + breakpoint aidee
 // raise(SIGINT);
 #include <stdint.h> // for uint64_t rather than unsigned long long
+#include <stdbool.h>
 #include "myomp.h"
 
 // data.table depends on R>=3.0.0 when R_xlen_t was introduced

src/init.c

@@ -76,6 +76,7 @@ SEXP fsort();
 SEXP inrange();
 SEXP between();
 SEXP hasOpenMP();
+SEXP uniqueNlogical();
 
 // .Externals
 SEXP fastmean();
@@ -154,6 +155,7 @@ R_CallMethodDef callMethods[] = {
 {"Cinrange", (DL_FUNC) &inrange, -1},
 {"Cbetween", (DL_FUNC) &between, -1},
 {"ChasOpenMP", (DL_FUNC) &hasOpenMP, -1},
+{"CuniqueNlogical", (DL_FUNC) &uniqueNlogical, -1},
 {NULL, NULL, 0}
 };
 

src/uniqlist.c

@@ -228,3 +228,28 @@ SEXP nestedid(SEXP l, SEXP cols, SEXP order, SEXP grps, SEXP resetvals, SEXP mul
   UNPROTECT(1);
   return(ans);
 }
+
+SEXP uniqueNlogical(SEXP x, SEXP narmArg) {
+  // single pass; short-circuit and return as soon as all 3 values are found
+  if (!isLogical(x)) error("x is not a logical vector");
+  if (!isLogical(narmArg) || length(narmArg)!=1 || INTEGER(narmArg)[0]==NA_INTEGER) error("na.rm must be TRUE or FALSE");
+  bool narm = LOGICAL(narmArg)[0]==1;
+  const R_xlen_t n = xlength(x);
+  if (n==0)
+    return ScalarInteger(0);  // empty vector
+  Rboolean first = LOGICAL(x)[0];
+  R_xlen_t i=0;
+  while (++i<n && LOGICAL(x)[i]==first);
+  if (i==n)
+    return ScalarInteger(first==NA_INTEGER && narm ? 0 : 1); // all one value
+  Rboolean second = LOGICAL(x)[i];
+  // we've found 2 different values (first and second). Which one didn't we find? Then just look for that.
+  // NA_LOGICAL == INT_MIN checked in init.c
+  const int third = (first+second == 1) ? NA_LOGICAL : ( first+second == INT_MIN ? TRUE : FALSE );
+  if (third==NA_LOGICAL && narm)
+    return ScalarInteger(2);  // TRUE and FALSE found before any NA, but na.rm=TRUE so we're done
+  while (++i<n) if (LOGICAL(x)[i]==third)
+    return ScalarInteger(3-narm);
+  return ScalarInteger(2-(narm && third!=NA_LOGICAL));
+}
+