feat: Implement arrow relations for formal contexts in C++ and expand concept lattice plotting with viewer and theme options.

Author: neuroimaginador

NEWS.md

@@ -1,5 +1,26 @@
 # fcaR 1.7.0
 
+New Functionality:
+
+* **Arrow Relations:** Added `calculate_arrow_relations()` method to `FormalContext` to compute the arrow relations ($\swarrow$, $\nearrow$, $\updownarrow$) of a binary formal context using a high-performance C++ implementation based on bitsets.
+* **Structural Analysis:** Added new methods to `FormalContext` for advanced structural analysis based on arrow relations:
+    * `is_distributive()`: Efficiently check if the concept lattice is distributive without computing it.
+    * `get_irreducible_objects()` / `get_irreducible_attributes()`: Identify the core elements needed to reconstruct the lattice.
+    * `get_core()`: Extract the smallest context that generates the same lattice.
+* **Optimized Reduction:** Added `reduce_arrows()` to `FormalContext`. This method clarifies and reduces a context using arrow relations, which is significantly faster than traditional methods for large contexts.
+* **Lattice Plotting Enhancements:**
+    * **Grade Balancing:** New `balance_grades` algorithm to improve visual symmetry in Hasse diagrams (e.g., for $N_5$).
+    * **Base R Viewer:** Added `viewer = "base"` to `plot()`, providing a lightweight alternative to `ggraph` with support for themes (`"standard"`, `"nord"`, `"vibrant"`, `"latex"`).
+    * **Vertical Alignment:** Sugiyama layout now correctly aligns single-node chains vertically.
+
+Improvements:
+
+* **Refactored `standardize()` and `reduce()`**: These methods now use `reduce_arrows()` internally, removing the dependency on pre-calculating the concept lattice and improving performance while preserving original labels.
+* **C++ Layout Engine**: Updated `calculate_lattice_layout_rcpp` to support numeric (decimal) Y coordinates for smooth vertical positioning.
+* **Internal helpers:** Added `.print_arrows()` to handle symbol mapping for both CLI (Unicode) and LaTeX output.
+* **Expanded Documentation:** Updated the `lattice_properties` vignette with a detailed section on arrow relations.
+* **Enhanced Testing:** Added `test-arrow_relations.R` and `test-arrow_advanced.R` with comprehensive unit tests.
+
 # fcaR 1.6.0
 
 New Functionality:

R/RcppExports.R

@@ -85,6 +85,19 @@ bonds_mcis_cpp <- function(extents, intents, verbose = FALSE) {
     .Call(`_fcaR_bonds_mcis_cpp`, extents, intents, verbose)
 }
 
+#' @title compute_arrow_relations_cpp
+#' @description Computes the arrow relations (swarrow, nearrow, and double arrow)
+#' for a binary formal context.
+#' @param I (IntegerMatrix) The binary incidence matrix of the formal context.
+#' @return An IntegerMatrix where:
+#'   - 1: \swarrow
+#'   - 2: \nearrow
+#'   - 3: \updownarrow
+#' @noRd
+compute_arrow_relations_cpp <- function(I) {
+    .Call(`_fcaR_compute_arrow_relations_cpp`, I)
+}
+
 print_matrix <- function(I) {
     invisible(.Call(`_fcaR_print_matrix`, I))
 }
@@ -177,8 +190,8 @@ calculate_grades_rcpp <- function(concept_ids, edge_from, edge_to) {
     .Call(`_fcaR_calculate_grades_rcpp`, concept_ids, edge_from, edge_to)
 }
 
-calculate_lattice_layout_rcpp <- function(concept_ids, grades, edge_from, edge_to, method) {
-    .Call(`_fcaR_calculate_lattice_layout_rcpp`, concept_ids, grades, edge_from, edge_to, method)
+calculate_lattice_layout_rcpp <- function(concept_ids, layers_vec, y_coords_vec, edge_from, edge_to, method) {
+    .Call(`_fcaR_calculate_lattice_layout_rcpp`, concept_ids, layers_vec, y_coords_vec, edge_from, edge_to, method)
 }
 
 binary_lincbo_implications <- function(I, save_concepts = FALSE, verbose = FALSE) {

R/concept_lattice.R

@@ -74,16 +74,24 @@ ConceptLattice <- R6::R6Class(
     #'   \item \code{"attributes"}: Nodes show only their intent (attributes).
     #'   \item \code{"empty"}: Nodes are drawn as points without labels. Recommended for very large lattices (>50 concepts).
     #' }
-    #' @param ...          Other parameters passed to the internal plotting function (e.g., graphical parameters for \code{ggraph}).
+    #' @param viewer       (character) The viewer to use for plotting. Options are:
+    #' \itemize{
+    #'   \item \code{"ggraph"} (default): Use \code{ggraph} for drawing.
+    #'   \item \code{"base"}: Use R base graphics. This is a lightweight alternative that supports themes.
+    #' }
+    #' @param theme        (character) The color theme to use for the \code{"base"} viewer. Options are: \code{"standard"}, \code{"nord"}, \code{"latex"}, \code{"vibrant"}.
+    #' @param ...          Other parameters passed to the internal plotting function (e.g., graphical parameters for \code{ggraph} or \code{base}).
     #'
-    #' @return If \code{to_latex} is \code{FALSE}, it returns (invisibly) the \code{ggplot2} object representing the graph.
+    #' @return If \code{to_latex} is \code{FALSE}, it returns (invisibly) the \code{ggplot2} object representing the graph (for \code{ggraph}) or \code{NULL} (for \code{base}).
     #' If \code{to_latex} is \code{TRUE}, it returns a \code{tikz_code} object containing the LaTeX code.
     #' @export
     plot = function(
       object_names = TRUE,
       to_latex = FALSE,
       method = c("sugiyama", "force"),
       mode = NULL,
+      viewer = c("ggraph", "base"),
+      theme = "standard",
       ...
     ) {
       # 1. Verificación de estado
@@ -111,6 +119,7 @@ ConceptLattice <- R6::R6Class(
       # 3. Delegación a lattice_plot
       # Pasamos los datos privados necesarios (matriz, objetos, atributos)
       method <- match.arg(method)
+      viewer <- match.arg(viewer)
       lattice_plot(
         nodes_df = nodes_df,
         cover_matrix = private$covering_matrix,
@@ -125,6 +134,8 @@ ConceptLattice <- R6::R6Class(
         intents = intents_list,
         object_names = self$objects,
         to_latex = to_latex,
+        viewer = viewer,
+        theme = theme,
         ...
       )
     },