clarify output indexing and boundary handling in fnn

NEWS.md

@@ -1,5 +1,9 @@
 # pc 0.3
 
+### enhancements
+
+* Clarify output indexing and boundary handling in `fnn` generic (#69).
+
 # pc 0.2
 
 ### new

R/fnn.R

@@ -1,4 +1,4 @@
-.fnn_ts = \(data, target, E = 2:10, k = 1, tau = 1, style = 1, lib = NULL, pred = NULL,
+.fnn_ts = \(data, target, E = 10, k = 1, tau = 1, style = 1, lib = NULL, pred = NULL,
             dist.metric = c("euclidean", "manhattan", "maximum"), rt = 10, eps = NULL,
             threads = length(E), higher.parallel = TRUE, ...) {
   dist.metric = match.arg(dist.metric)
@@ -11,7 +11,7 @@
                  k, threads, higher.parallel, NULL, NULL))
 }
 
-.fnn_lattice = \(data, target, E = 3:10, k = 1, tau = 1, style = 1, lib = NULL, pred = NULL, 
+.fnn_lattice = \(data, target, E = 10, k = 1, tau = 1, style = 1, lib = NULL, pred = NULL, 
                  dist.metric = c("euclidean", "manhattan", "maximum"), rt = 10, eps = NULL,
                  threads = length(E), higher.parallel = TRUE, detrend = FALSE, nb = NULL, ...) {
   if (is.null(nb)) nb = sdsfun::spdep_nb(data)
@@ -25,7 +25,7 @@
                  k, threads, higher.parallel, nb, NULL))
 }
 
-.fnn_grid = \(data, target, E = 3:10, k = 1, tau = 1, style = 1, lib = NULL, pred = NULL, 
+.fnn_grid = \(data, target, E = 10, k = 1, tau = 1, style = 1, lib = NULL, pred = NULL, 
               dist.metric = c("euclidean", "manhattan", "maximum"), rt = 10, eps = NULL, 
               threads = length(E), higher.parallel = TRUE, detrend = FALSE, ...) {
   dist.metric = match.arg(dist.metric)

src/FNN.cpp

@@ -261,9 +261,9 @@ Rcpp::NumericVector RcppFNN(
     result.names() = resnames;
 
     // Terminal-friendly hint (one-time, non-intrusive)
-    Rcpp::Rcout << "[fnn] Output 'E:i' corresponds to the i-th valid embedding dimension.\n"
-                << "[fnn] Input E values exceeding max embeddable dimension were truncated.\n"
-                << "[fnn] Please map output indices to original E inputs before interpretation.\n";
+    Rcpp::Rcout << "[fnn] Input E values exceeding max embeddable dimension were truncated, and values < 2 were clamped to 2.\n"
+                << "[fnn] Max embedding dimension E_max is auto-computed, with results returned for dimensions 1 through E_max.\n"
+                << "[fnn] Output 'E:i' (where i = 1 to E_max-1) corresponds to the comparison between dimension i and i+1.\n";
 
     return result;
 }