From 980c0dd360b5454d49df47e08b8708ff888ae7a4 Mon Sep 17 00:00:00 2001
From: marcandre <marcandre@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Mon, 20 Nov 2017 02:18:34 +0000
Subject: lib/matrix: Add Matrix{.|#}combine

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60859 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 lib/matrix.rb              | 29 +++++++++++++++++++++++++++++
 test/matrix/test_matrix.rb | 17 +++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/lib/matrix.rb b/lib/matrix.rb
index 0a2b609b59..2f2d0f371a 100644
--- a/lib/matrix.rb
+++ b/lib/matrix.rb
@@ -249,6 +249,35 @@ class Matrix
     new result, total_column_count
   end
 
+  #
+  # Create a matrix by combining matrices entrywise, using the given block
+  #
+  #   x = Matrix[[6, 6], [4, 4]]
+  #   y = Matrix[[1, 2], [3, 4]]
+  #   Matrix.combine(x, y) {|a, b| a - b} # => Matrix[[5, 4], [1, 2]]
+  #
+  def Matrix.combine(*matrices)
+    return to_enum(__method__, *matrices) unless block_given?
+
+    return Matrix.empty if matrices.empty?
+    matrices.map!(&CoercionHelper.method(:coerce_to_matrix))
+    x = matrices.first
+    matrices.each do |m|
+      Matrix.Raise ErrDimensionMismatch unless x.row_count == m.row_count && x.column_count == m.column_count
+    end
+
+    rows = Array.new(x.row_count) do |i|
+      Array.new(x.column_count) do |j|
+        yield matrices.map{|m| m[i,j]}
+      end
+    end
+    new rows, x.column_count
+  end
+
+  def combine(*matrices, &block)
+    Matrix.combine(self, *matrices, &block)
+  end
+
   #
   # Matrix.new is private; use Matrix.rows, columns, [], etc... to create.
   #
diff --git a/test/matrix/test_matrix.rb b/test/matrix/test_matrix.rb
index 5b0bc968f7..92a24d1e9f 100644
--- a/test/matrix/test_matrix.rb
+++ b/test/matrix/test_matrix.rb
@@ -592,6 +592,23 @@ class TestMatrix < Test::Unit::TestCase
     assert_equal Matrix[[1],[2],[3]], Matrix.vstack(Vector[1,2], Vector[3])
   end
 
+  def test_combine
+    x = Matrix[[6, 6], [4, 4]]
+    y = Matrix[[1, 2], [3, 4]]
+    assert_equal Matrix[[5, 4], [1, 0]], Matrix.combine(x, y) {|a, b| a - b}
+    assert_equal Matrix[[5, 4], [1, 0]], x.combine(y) {|a, b| a - b}
+    # Without block
+    assert_equal Matrix[[5, 4], [1, 0]], Matrix.combine(x, y).each {|a, b| a - b}
+    # With vectors
+    assert_equal Matrix[[111], [222]], Matrix.combine(Matrix[[1], [2]], Vector[10,20], Vector[100,200], &:sum)
+    # Basic checks
+    assert_raise(Matrix::ErrDimensionMismatch) { @m1.combine(x) { raise } }
+    # Edge cases
+    assert_equal Matrix.empty, Matrix.combine{ raise }
+    assert_equal Matrix.empty(3,0), Matrix.combine(Matrix.empty(3,0), Matrix.empty(3,0)) { raise }
+    assert_equal Matrix.empty(0,3), Matrix.combine(Matrix.empty(0,3), Matrix.empty(0,3)) { raise }
+  end
+
   def test_eigenvalues_and_eigenvectors_symmetric
     m = Matrix[
       [8, 1],
-- 
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