Allow QgsStringStatisticalSummary to calculate mean string length

Author: nyalldawson

python/core/qgsstringstatisticalsummary.sip

@@ -31,6 +31,7 @@ class QgsStringStatisticalSummary
       Max, //!< Maximum string value
       MinimumLength, //!< Minimum length of string
       MaximumLength, //!< Maximum length of string
+      MeanLength, //!< Mean length of strings
       All, //! All statistics
     };
     typedef QFlags<QgsStringStatisticalSummary::Statistic> Statistics;
@@ -147,6 +148,12 @@ class QgsStringStatisticalSummary
      */
     int maxLength() const;
 
+    /**
+      * Returns the mean length of strings.
+      * @note added in QGIS 3.0
+      */
+    double meanLength() const;
+
     /** Returns the friendly display name for a statistic
      * @param statistic statistic to return name for
      */

src/core/qgsstringstatisticalsummary.cpp

@@ -42,6 +42,8 @@ void QgsStringStatisticalSummary::reset()
   mMax.clear();
   mMinLength = INT_MAX;
   mMaxLength = 0;
+  mSumLengths = 0;
+  mMeanLength = 0;
 }
 
 void QgsStringStatisticalSummary::calculate( const QStringList& values )
@@ -71,8 +73,7 @@ void QgsStringStatisticalSummary::addValue( const QVariant& value )
 
 void QgsStringStatisticalSummary::finalize()
 {
-  //nothing to do for now - this method has been added for forward compatibility
-  //if statistics are implemented which require a post-calculation step
+  mMeanLength = mSumLengths / static_cast< double >( mCount );
 }
 
 void QgsStringStatisticalSummary::calculateFromVariants( const QVariantList& values )
@@ -121,6 +122,8 @@ void QgsStringStatisticalSummary::testString( const QString& string )
       mMax = string;
     }
   }
+  if ( mStatistics & MeanLength )
+    mSumLengths += string.length();
   mMinLength = qMin( mMinLength, string.length() );
   mMaxLength = qMax( mMaxLength, string.length() );
 }
@@ -143,6 +146,8 @@ QVariant QgsStringStatisticalSummary::statistic( QgsStringStatisticalSummary::St
       return mMinLength;
     case MaximumLength:
       return mMaxLength;
+    case MeanLength:
+      return mMeanLength;
     case All:
       return 0;
   }
@@ -167,6 +172,8 @@ QString QgsStringStatisticalSummary::displayName( QgsStringStatisticalSummary::S
       return QObject::tr( "Minimum length" );
     case MaximumLength:
       return QObject::tr( "Maximum length" );
+    case MeanLength:
+      return QObject::tr( "Mean length" );
     case All:
       return QString();
   }

src/core/qgsstringstatisticalsummary.h

@@ -51,7 +51,8 @@ class CORE_EXPORT QgsStringStatisticalSummary
       Max = 16, //!< Maximum string value
       MinimumLength = 32, //!< Minimum length of string
       MaximumLength = 64, //!< Maximum length of string
-      All = Count | CountDistinct | CountMissing | Min | Max, //! All statistics
+      MeanLength = 128, //!< Mean length of strings
+      All = Count | CountDistinct | CountMissing | Min | Max | MinimumLength | MaximumLength | MeanLength, //! All statistics
     };
     Q_DECLARE_FLAGS( Statistics, Statistic )
 
@@ -167,6 +168,12 @@ class CORE_EXPORT QgsStringStatisticalSummary
      */
     int maxLength() const { return mMaxLength; }
 
+    /**
+      * Returns the mean length of strings.
+      * @note added in QGIS 3.0
+      */
+    double meanLength() const { return mMeanLength; }
+
     /** Returns the friendly display name for a statistic
      * @param statistic statistic to return name for
      */
@@ -183,6 +190,8 @@ class CORE_EXPORT QgsStringStatisticalSummary
     QString mMax;
     int mMinLength;
     int mMaxLength;
+    long mSumLengths;
+    double mMeanLength;
 
     void testString( const QString& string );
 };

tests/src/python/test_qgsstringstatisticalsummary.py

@@ -48,6 +48,8 @@ def testStats(self):
         self.assertEqual(s2.minLength(), 0)
         self.assertEqual(s.maxLength(), 8)
         self.assertEqual(s2.maxLength(), 8)
+        self.assertEqual(s.meanLength(), 3.33333333333333333333333)
+        self.assertEqual(s2.meanLength(), 3.33333333333333333333333)
 
         #extra check for minLength without empty strings
         s.calculate(['1111111', '111', '11111'])
@@ -63,6 +65,7 @@ def testIndividualStats(self):
                  {'stat': QgsStringStatisticalSummary.Max, 'expected': 'eeee'},
                  {'stat': QgsStringStatisticalSummary.MinimumLength, 'expected': 0},
                  {'stat': QgsStringStatisticalSummary.MaximumLength, 'expected': 8},
+                 {'stat': QgsStringStatisticalSummary.MeanLength, 'expected': 3.3333333333333335},
                  ]
 
         s = QgsStringStatisticalSummary()