[FEATURE] Add generate_series(start,stop,step) expression function

The function creates an array containing a sequence of numbers.

Author: nirvn

resources/function_help/json/generate_series

@@ -0,0 +1,13 @@
+{
+  "name": "generate_series",
+  "type": "function",
+  "description": "Creates an array containing a sequence of numbers.",
+  "arguments": [
+    {"arg":"start", "description":"first value of the sequence"},
+    {"arg":"stop", "description":"value that ends the sequence once reached"},
+    {"arg":"step","optional":true,"default":"1","description":"value used as the increment between values"}
+  ],
+  "examples": [ { "expression":"generate_series('1,5)", "returns":"array: '1', '2', '3', '4', '5'"},
+                { "expression":"generate_series('5,1,-1)", "returns":"array: '5', '4', '3', '2', '1'"}
+  ]
+}

src/core/expression/qgsexpressionfunction.cpp

@@ -220,6 +220,30 @@ bool QgsExpressionFunction::allParamsStatic( const QgsExpressionNodeFunction *no
   return true;
 }
 
+static QVariant fcnGenerateSeries( const QVariantList &values, const QgsExpressionContext *, QgsExpression *parent, const QgsExpressionNodeFunction * )
+{
+  double start = QgsExpressionUtils::getDoubleValue( values.at( 0 ), parent );
+  double stop = QgsExpressionUtils::getDoubleValue( values.at( 1 ), parent );
+  double step = QgsExpressionUtils::getDoubleValue( values.at( 2 ), parent );
+
+  if ( step == 0.0  || ( step > 0.0 && start > stop ) || ( step < 0.0 && start < stop ) )
+    return QVariant();
+
+  QVariantList array;
+  int length = 1;
+
+  array << start;
+  double current = start + step;
+  while ( ( ( step > 0.0 && current <= stop ) || ( step < 0.0 && current >= stop ) ) && length <= 1000000 )
+  {
+    array << current;
+    current += step;
+    length++;
+  }
+
+  return array;
+}
+
 static QVariant fcnGetVariable( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction * )
 {
   if ( !context )
@@ -4724,6 +4748,7 @@ const QList<QgsExpressionFunction *> &QgsExpression::Functions()
         << new QgsStaticExpressionFunction( QStringLiteral( "array_distinct" ), 1, fcnArrayDistinct, QStringLiteral( "Arrays" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "array_to_string" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "array" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "delimiter" ), true, "," ) << QgsExpressionFunction::Parameter( QStringLiteral( "emptyvalue" ), true, "" ), fcnArrayToString, QStringLiteral( "Arrays" ) )
         << new QgsStaticExpressionFunction( QStringLiteral( "string_to_array" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "string" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "delimiter" ), true, "," ) << QgsExpressionFunction::Parameter( QStringLiteral( "emptyvalue" ), true, "" ), fcnStringToArray, QStringLiteral( "Arrays" ) )
+        << new QgsStaticExpressionFunction( QStringLiteral( "generate_series" ), QgsExpressionFunction::ParameterList() << QgsExpressionFunction::Parameter( QStringLiteral( "start" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "stop" ) ) << QgsExpressionFunction::Parameter( QStringLiteral( "step" ), true, 1.0 ), fcnGenerateSeries, QStringLiteral( "Arrays" ) )
 
         //functions for maps
         << new QgsStaticExpressionFunction( QStringLiteral( "map" ), -1, fcnMap, QStringLiteral( "Maps" ) )

tests/src/core/testqgsexpression.cpp

@@ -2607,6 +2607,23 @@ class TestQgsExpression: public QObject
       QCOMPARE( v4, QVariant( "test value" ) );
     }
 
+    void eval_generate_series()
+    {
+      QVariantList array;
+      array << 1 << 2 << 3 << 4;
+      QCOMPARE( QgsExpression( "generate_series(1,4)" ).evaluate(), QVariant( array ) );
+      array.clear();
+      array << 1 << 1.25 << 1.5 << 1.75 << 2;
+      QCOMPARE( QgsExpression( "generate_series(1,2,0.25)" ).evaluate(), QVariant( array ) );
+      array.clear();
+      array << 10 << 9 << 8;
+      QCOMPARE( QgsExpression( "generate_series(10,8,-1)" ).evaluate(), QVariant( array ) );
+
+      QCOMPARE( QgsExpression( "generate_series(10,11,-1)" ).evaluate(), QVariant() );
+      QCOMPARE( QgsExpression( "generate_series(10,5)" ).evaluate(), QVariant() );
+      QCOMPARE( QgsExpression( "generate_series(1,2,0)" ).evaluate(), QVariant() );
+    }
+
     void eval_string_array()
     {
       QgsFeature f( 100 );