Do not calculate median if only one variable is provided.

Fixes https://trac.osgeo.org/grass/ticket/3296


git-svn-id: https://svn.osgeo.org/grass/grass/trunk@70674 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/calc/xnmedian.c

@@ -82,6 +82,8 @@ int f_nmedian(int argc, const int *argt, void **args)
 
 		if (!n)
 		    SET_NULL_C(&res[i]);
+                else if (n == 1)
+                    res[i] = *a1;
 		else {
 		    qsort(a, n, sizeof(CELL), icmp);
 		    res[i] = (*a1 + *a2) / 2;
@@ -109,6 +111,8 @@ int f_nmedian(int argc, const int *argt, void **args)
 
 		if (!n)
 		    SET_NULL_F(&res[i]);
+                else if (n == 1)
+                    res[i] = *a1;
 		else {
 		    qsort(a, n, sizeof(FCELL), fcmp);
 		    res[i] = (*a1 + *a2) / 2;
@@ -136,6 +140,8 @@ int f_nmedian(int argc, const int *argt, void **args)
 
 		if (!n)
 		    SET_NULL_D(&res[i]);
+                else if (n == 1)
+                    res[i] = *a1;
 		else {
 		    qsort(a, n, sizeof(DCELL), dcmp);
 		    res[i] = (*a1 + *a2) / 2;

raster/r.mapcalc/testsuite/test_nmedian_bug_3296.py

@@ -0,0 +1,104 @@
+#!/usr/bin/env python
+
+############################################################################
+#
+# MODULE:        test_nmedian_bug.py
+# AUTHOR:        Maris Nartiss, based on Vaclav Petras test_row_above_below_bug.py
+# PURPOSE:       Show bug reported in #3296
+# COPYRIGHT:     (C) 2017 by Maris Nartiss and the GRASS Development Team
+#
+#                This program is free software under the GNU General Public
+#                License (>=v2). Read the file COPYING that comes with GRASS
+#                for details.
+#
+#############################################################################
+
+# #3296
+# r.mapcalc calculates wrong median value if one of two input maps has a null value
+# Also depends on correct functioning of row() and col() mapcalc variables
+# https://trac.osgeo.org/grass/ticket/3296
+
+from grass.gunittest.case import TestCase
+from grass.gunittest.main import test
+
+
+OUTPUT = """\
+north: 3
+south: 0
+west: 0
+east: 3
+rows: 3
+cols: 3
+null: *
+1.0 1.0 1.0
+4.0 4.0 4.0
+9.0 9.0 9.0
+"""
+
+OUTPUT_CELL = """\
+north: 3
+south: 0
+west: 0
+east: 3
+rows: 3
+cols: 3
+null: *
+1 1 1
+4 4 4
+9 9 9
+"""
+
+
+class TestNmedianBug(TestCase):
+    to_remove = []
+    input = 'r_mapcalc_test_pattern'
+    output = 'r_mapcalc_test_output'
+    output_ref = 'r_mapcalc_test_output_ref'
+    output_cell = 'r_mapcalc_test_output_cell'
+
+    def setUp(self):
+        expression = "{o}=row()*col()".format(o=self.input)
+        self.use_temp_region()
+        self.runModule('g.region', n=3, s=0, e=3, w=0, res=1)
+        self.runModule('r.mapcalc', expression=expression, overwrite=True)
+        self.to_remove.append(self.input)
+        self.runModule('r.in.ascii', input='-', stdin_=OUTPUT,
+                       output=self.output_ref, overwrite=True)
+        self.to_remove.append(self.output_ref)
+        self.runModule('r.in.ascii', input='-', stdin_=OUTPUT_CELL,
+                       output=self.output_cell, overwrite=True)
+        self.to_remove.append(self.output_cell)
+
+    def tearDown(self):
+        self.del_temp_region()
+        if 0 and self.to_remove:
+            self.runModule('g.remove', flags='f', type='raster',
+                           name=','.join(self.to_remove), verbose=True)
+
+    def test_cell(self):
+        expression = "{o}=nmedian(({i}[0,-1] - {i})^2,({i}[0,1] - {i})^2)".format(o=self.output, i=self.input)
+        self.assertModule('r.mapcalc', expression=expression, overwrite=True)
+        self.assertRasterExists(self.output)
+        self.to_remove.append(self.output)
+        self.assertRastersNoDifference(actual=self.output,
+            reference=self.output_cell, precision=0)
+
+    def test_fcell(self):
+        expression = "{o}=nmedian(float(({i}[0,-1] - {i})^2), float(({i}[0,1] - {i})^2))".format(o=self.output, i=self.input)
+        self.assertModule('r.mapcalc', expression=expression, overwrite=True)
+        self.assertRasterExists(self.output)
+        self.to_remove.append(self.output)
+        self.assertRastersNoDifference(actual=self.output,
+            reference=self.output_ref, precision=0)
+    
+    def test_dcell(self):
+        expression = "{o}=nmedian(double(({i}[0,-1] - {i})^2), double(({i}[0,1] - {i})^2))".format(o=self.output, i=self.input)
+        self.assertModule('r.mapcalc', expression=expression, overwrite=True)
+        self.assertRasterExists(self.output)
+        self.to_remove.append(self.output)
+        self.assertRastersNoDifference(actual=self.output,
+            reference=self.output_ref, precision=0)
+
+
+if __name__ == '__main__':
+    test()