diff --git a/src/backend/datasources/filters/NgspiceRawAsciiFilter.cpp b/src/backend/datasources/filters/NgspiceRawAsciiFilter.cpp
index a874e63ba..0186df198 100644
--- a/src/backend/datasources/filters/NgspiceRawAsciiFilter.cpp
+++ b/src/backend/datasources/filters/NgspiceRawAsciiFilter.cpp
@@ -1,301 +1,387 @@
 /***************************************************************************
 File                 : NgspiceRawAsciiFilter.cpp
 Project              : LabPlot
 Description          : Ngspice RAW ASCII filter
 --------------------------------------------------------------------
 Copyright            : (C) 2018 Alexander Semke (alexander.semke@web.de)
 ***************************************************************************/
 
 /***************************************************************************
 *                                                                         *
 *  This program is free software; you can redistribute it and/or modify   *
 *  it under the terms of the GNU General Public License as published by   *
 *  the Free Software Foundation; either version 2 of the License, or      *
 *  (at your option) any later version.                                    *
 *                                                                         *
 *  This program is distributed in the hope that it will be useful,        *
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of         *
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the          *
 *  GNU General Public License for more details.                           *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the Free Software           *
 *   Foundation, Inc., 51 Franklin Street, Fifth Floor,                    *
 *   Boston, MA  02110-1301  USA                                           *
 *                                                                         *
 ***************************************************************************/
 #include "backend/datasources/LiveDataSource.h"
 #include "backend/datasources/filters/NgspiceRawAsciiFilter.h"
 #include "backend/datasources/filters/NgspiceRawAsciiFilterPrivate.h"
 #include "backend/lib/trace.h"
 
 #include <QFile>
 
 /*!
 \class NgspiceRawAsciiFilter
 \brief Import of data stored in Ngspice's raw formant, ASCCI version of it.
 
 \ingroup datasources
 */
 NgspiceRawAsciiFilter::NgspiceRawAsciiFilter() : AbstractFileFilter(), d(new NgspiceRawAsciiFilterPrivate(this)) {}
 
 NgspiceRawAsciiFilter::~NgspiceRawAsciiFilter() {}
 
 bool NgspiceRawAsciiFilter::isNgspiceAsciiFile(const QString& fileName) {
 	QFile file(fileName);
     if (!file.open(QIODevice::ReadOnly | QIODevice::Text)) {
 		DEBUG("Failed to open the file " << fileName.toStdString());
 		return false;
 	}
 
 	QString line = file.readLine();
 	if (!line.startsWith(QLatin1String("Title:")))
 		return false;
 
 	line = file.readLine();
 	if (!line.startsWith(QLatin1String("Date:")))
 		return false;
 
 	line = file.readLine();
 	if (!line.startsWith(QLatin1String("Plotname:")))
 		return false;
 
 	line = file.readLine();
 	if (!line.startsWith(QLatin1String("Flags:")))
 		return false;
 
 	line = file.readLine();
 	if (!line.startsWith(QLatin1String("No. Variables:")))
 		return false;
 
 	line = file.readLine();
 	if (!line.startsWith(QLatin1String("No. Points:")))
 		return false;
 
 	line = file.readLine();
 	if (!line.startsWith(QLatin1String("Variables:")))
 		return false;
 
 	return true;
 }
 
 QString NgspiceRawAsciiFilter::fileInfoString(const QString& fileName) {
 	QFile file(fileName);
     if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
 		return QString();
 
 	QString info;
 	while (!file.atEnd()) {
 		QString line = file.readLine();
 		if (line.simplified() == QLatin1String("Values:"))
 			break;
 
 		if (!info.isEmpty())
 			info += QLatin1String("<br>");
 
 		info += line;
 	}
 
 	return info;
 }
 
-
 /*!
   reads the content of the file \c fileName.
 */
 QVector<QStringList> NgspiceRawAsciiFilter::readDataFromFile(const QString& fileName, AbstractDataSource* dataSource, AbstractFileFilter::ImportMode importMode, int lines) {
 	d->readDataFromFile(fileName, dataSource, importMode, lines);
 	return QVector<QStringList>();  //TODO: remove this later once all read*-functions in the filter classes don't return any preview strings anymore
 }
 
 QVector<QStringList> NgspiceRawAsciiFilter::preview(const QString& fileName, int lines) {
 	return d->preview(fileName, lines);
 }
 
 /*!
   writes the content of the data source \c dataSource to the file \c fileName.
 */
 void NgspiceRawAsciiFilter::write(const QString& fileName, AbstractDataSource* dataSource) {
 	d->write(fileName, dataSource);
 }
 
 /*!
   loads the predefined filter settings for \c filterName
 */
 void NgspiceRawAsciiFilter::loadFilterSettings(const QString& filterName) {
 	Q_UNUSED(filterName);
 }
 
 /*!
   saves the current settings as a new filter with the name \c filterName
 */
 void NgspiceRawAsciiFilter::saveFilterSettings(const QString& filterName) const {
 	Q_UNUSED(filterName);
 }
 
-
 void NgspiceRawAsciiFilter::setStartRow(const int r) {
 	d->startRow = r;
 }
 int NgspiceRawAsciiFilter::startRow() const {
 	return d->startRow;
 }
 
 void NgspiceRawAsciiFilter::setEndRow(const int r) {
 	d->endRow = r;
 }
 int NgspiceRawAsciiFilter::endRow() const {
 	return d->endRow;
 }
 
 void NgspiceRawAsciiFilter::setStartColumn(const int c) {
 	d->startColumn = c;
 }
 int NgspiceRawAsciiFilter::startColumn() const {
 	return d->startColumn;
 }
 
 void NgspiceRawAsciiFilter::setEndColumn(const int c) {
 	d->endColumn = c;
 }
 int NgspiceRawAsciiFilter::endColumn() const {
 	return d->endColumn;
 }
 
 QStringList NgspiceRawAsciiFilter::vectorNames() const {
 	return d->vectorNames;
 }
 
 QVector<AbstractColumn::ColumnMode> NgspiceRawAsciiFilter::columnModes() {
 	return d->columnModes;
 }
 
 //#####################################################################
 //################### Private implementation ##########################
 //#####################################################################
 NgspiceRawAsciiFilterPrivate::NgspiceRawAsciiFilterPrivate(NgspiceRawAsciiFilter* owner) : q(owner),
 	startRow(1),
 	endRow(-1),
 	startColumn(1),
-	endColumn(-1),
-	m_actualStartRow(1),
-	m_actualRows(0),
-	m_actualCols(0),
-	m_prepared(false),
-	m_columnOffset(0) {
+	endColumn(-1) {
 }
 
 /*!
     reads the content of the file \c fileName to the data source \c dataSource. Uses the settings defined in the data source.
 */
 void NgspiceRawAsciiFilterPrivate::readDataFromFile(const QString& fileName, AbstractDataSource* dataSource, AbstractFileFilter::ImportMode importMode, int lines) {
 	DEBUG("NgspiceRawAsciiFilterPrivate::readDataFromFile(): fileName = \'" << fileName.toStdString() << "\', dataSource = "
 	      << dataSource << ", mode = " << ENUM_TO_STRING(AbstractFileFilter, ImportMode, importMode) << ", lines = " << lines);
 
+	QFile file(fileName);
+    if (!file.open(QIODevice::ReadOnly | QIODevice::Text)) {
+		DEBUG("Failed to open the file " << fileName.toStdString());
+		return;
+	}
+
+	//skip the first four lines in the header
+	file.readLine();
+	file.readLine();
+	file.readLine();
+	file.readLine();
+
+	//number of variables
+	QString line = file.readLine();
+	const int vars = line.right(line.length() - 15).toInt(); //remove the "No. Variables: " sub-string
+
+	//number of points
+	line = file.readLine();
+	const int points = line.right(line.length() - 12).toInt(); //remove the "No. Points: " sub-string
+
+	//add names of the variables
+	vectorNames.clear();
+	columnModes.clear();
+	file.readLine();
+	for (int i = 0; i<vars; ++i) {
+		line = file.readLine();
+		QStringList tokens = line.split('\t');
+		vectorNames << tokens.at(2) + QLatin1String(", ") + tokens.at(3).simplified();
+		columnModes << AbstractColumn::Numeric;
+	}
+
+	file.readLine(); //skip the line with "Values"
+
+	//read the first value to check whether we have complex numbers
+	qint64 pos = file.pos();
+	line = file.readLine();
+	bool hasComplexValues = (line.indexOf(QLatin1Char(',')) != -1);
+	if (hasComplexValues) {
+		//add column names and types for the imaginary parts
+		QStringList newVectorNames;
+		for (int i = 0; i<vars; ++i) {
+			columnModes << AbstractColumn::Numeric;
+			newVectorNames << vectorNames.at(i) + QLatin1String(" REAL");
+			newVectorNames << vectorNames.at(i) + QLatin1String(" IMAGINARY");
+		}
+		vectorNames = newVectorNames;
+	}
+	file.seek(pos);
+
+	//prepare the data container
+	int actualRows = points;
+	int actualCols = vars;
+	if (hasComplexValues)
+		actualCols *= 2;
+
+	const int columnOffset = dataSource->prepareImport(m_dataContainer, importMode, actualRows - startRow + 1,
+		                 actualCols, vectorNames, columnModes);
+
+	//read the data points
+	QStringList lineString;
+	int currentRow = 0;	// indexes the position in the vector(column)
+	QLocale locale(QLocale::C);
+	bool isNumber(false);
+	for (int i = 0; i < points; ++i) {
+		lineString.clear();
+		for (int j = 0; j < vars; ++j) {
+			line = file.readLine();
+			QStringList tokens = line.split(QLatin1Char('\t'));
+			QString valueString = tokens.at(1).simplified(); //string containing the value(s)
+			if (hasComplexValues) {
+				QStringList realImgTokens = valueString.split(QLatin1Char(','));
+				if (realImgTokens.size() == 2) { //sanity check to make sure we really have both parts
+					//real part
+					double value = locale.toDouble(realImgTokens.at(0), &isNumber);
+					static_cast<QVector<double>*>(m_dataContainer[2*j])->operator[](currentRow) = (isNumber ? value : NAN);
+
+					//imaginary part
+					value = locale.toDouble(realImgTokens.at(0), &isNumber);
+					static_cast<QVector<double>*>(m_dataContainer[2*j+1])->operator[](currentRow) = (isNumber ? value : NAN);
+				}
+			} else {
+				const double value = locale.toDouble(valueString, &isNumber);
+				static_cast<QVector<double>*>(m_dataContainer[j])->operator[](currentRow) = (isNumber ? value : NAN);
+			}
+		}
+
+		file.readLine(); //skip the empty line after each value block
+
+		currentRow++;
+		emit q->completed(100 * currentRow/actualRows);
+	}
+
+	dataSource->finalizeImport(columnOffset, startColumn, endColumn, "", importMode);
 }
 
 /*!
  * generates the preview for the file \c fileName reading the provided number of \c lines.
  */
 QVector<QStringList> NgspiceRawAsciiFilterPrivate::preview(const QString& fileName, int lines) {
 	QVector<QStringList> dataStrings;
 
 	QFile file(fileName);
     if (!file.open(QIODevice::ReadOnly | QIODevice::Text)) {
 		DEBUG("Failed to open the file " << fileName.toStdString());
 		return dataStrings;
 	}
 
 	//skip the first four lines in the header
 	file.readLine();
 	file.readLine();
 	file.readLine();
 	file.readLine();
 
 	//number of variables
 	QString line = file.readLine();
-	int vars = line.right(line.length() - 15).toInt(); //remove the "No. Variables: " sub-string
+	const int vars = line.right(line.length() - 15).toInt(); //remove the "No. Variables: " sub-string
 
 	//number of points
 	line = file.readLine();
-	int points = line.right(line.length() - 12).toInt(); //remove the "No. Points: " sub-string
+	const int points = line.right(line.length() - 12).toInt(); //remove the "No. Points: " sub-string
 
 	//add names of the variables
 	vectorNames.clear();
 	columnModes.clear();
 	file.readLine();
 	for (int i = 0; i<vars; ++i) {
 		line = file.readLine();
 		QStringList tokens = line.split('\t');
 		vectorNames << tokens.at(2) + QLatin1String(", ") + tokens.at(3).simplified();
 		columnModes << AbstractColumn::Numeric;
 	}
 
 	file.readLine(); //skip the line with "Values"
 
 	//read the first value to check whether we have complex numbers
 	qint64 pos = file.pos();
 	line = file.readLine();
 	bool hasComplexValues = (line.indexOf(QLatin1Char(',')) != -1);
 	if (hasComplexValues) {
 		//add column names and types for the imaginary parts
 		QStringList newVectorNames;
 		for (int i = 0; i<vars; ++i) {
 			columnModes << AbstractColumn::Numeric;
 			newVectorNames << vectorNames.at(i) + QLatin1String(" REAL");
 			newVectorNames << vectorNames.at(i) + QLatin1String(" IMAGINARY");
 		}
 		vectorNames = newVectorNames;
 	}
 	file.seek(pos);
 
-	//add the data points
+	//read the data points
 	QStringList lineString;
 	for (int i = 0; i< qMin(lines, points); ++i) {
 		lineString.clear();
 		for (int j = 0; j < vars; ++j) {
 			line = file.readLine();
 			QStringList tokens = line.split(QLatin1Char('\t'));
 			QString value = tokens.at(1).simplified(); //string containing the value(s)
 			if (hasComplexValues) {
 				QStringList realImgTokens = value.split(QLatin1Char(','));
 				if (realImgTokens.size() == 2) { //sanity check to make sure we really have both parts
 					lineString << realImgTokens.at(0); //real part
-					lineString << realImgTokens.at(0); //imaginary part
+					lineString << realImgTokens.at(1); //imaginary part
 				}
 			} else
 				lineString << value;
 		}
 
 		dataStrings << lineString;
 		file.readLine(); //skip the empty line after each value block
 	}
 
 	return dataStrings;
 }
 
 /*!
     writes the content of \c dataSource to the file \c fileName.
 */
 void NgspiceRawAsciiFilterPrivate::write(const QString & fileName, AbstractDataSource* dataSource) {
 	Q_UNUSED(fileName);
 	Q_UNUSED(dataSource);
 }
 
 //##############################################################################
 //##################  Serialization/Deserialization  ###########################
 //##############################################################################
 /*!
   Saves as XML.
  */
 void NgspiceRawAsciiFilter::save(QXmlStreamWriter* writer) const {
 	Q_UNUSED(writer);
 }
 
 /*!
   Loads from XML.
 */
 bool NgspiceRawAsciiFilter::load(XmlStreamReader* reader) {
 	Q_UNUSED(reader);
 	return true;
 }
diff --git a/src/backend/datasources/filters/NgspiceRawAsciiFilterPrivate.h b/src/backend/datasources/filters/NgspiceRawAsciiFilterPrivate.h
index ef59a145d..001236eae 100644
--- a/src/backend/datasources/filters/NgspiceRawAsciiFilterPrivate.h
+++ b/src/backend/datasources/filters/NgspiceRawAsciiFilterPrivate.h
@@ -1,61 +1,56 @@
 /***************************************************************************
 File                 : NgspiceRawNgspiceRawAsciiFilterPrivate.h
 Project              : LabPlot
 Description          : Ngspice RAW ASCII filter
 --------------------------------------------------------------------
 Copyright            : (C) 2018 Alexander Semke (alexander.semke@web.de)
 ***************************************************************************/
 
 /***************************************************************************
  *                                                                         *
  *  This program is free software; you can redistribute it and/or modify   *
  *  it under the terms of the GNU General Public License as published by   *
  *  the Free Software Foundation; either version 2 of the License, or      *
  *  (at your option) any later version.                                    *
  *                                                                         *
  *  This program is distributed in the hope that it will be useful,        *
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of         *
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the          *
  *  GNU General Public License for more details.                           *
  *                                                                         *
  *   You should have received a copy of the GNU General Public License     *
  *   along with this program; if not, write to the Free Software           *
  *   Foundation, Inc., 51 Franklin Street, Fifth Floor,                    *
  *   Boston, MA  02110-1301  USA                                           *
  *                                                                         *
  ***************************************************************************/
 
 #ifndef NGSPICERAWASCIIFILTERPRIVATE_H
 #define NGSPICERAWASCIIFILTERPRIVATE_H
 
 class AbstractDataSource;
 
 class NgspiceRawAsciiFilterPrivate {
 
 public:
 	explicit NgspiceRawAsciiFilterPrivate(NgspiceRawAsciiFilter*);
 
 	void readDataFromFile(const QString& fileName, AbstractDataSource* = nullptr,
 	                      AbstractFileFilter::ImportMode = AbstractFileFilter::Replace, int lines = -1);
 	void write(const QString& fileName, AbstractDataSource*);
 	QVector<QStringList> preview(const QString& fileName, int lines);
 
 	const NgspiceRawAsciiFilter* q;
 
 	QStringList vectorNames;
 	QVector<AbstractColumn::ColumnMode> columnModes;
 	int startRow;
 	int endRow;
 	int startColumn;
 	int endColumn;
 
 private:
-	int m_actualStartRow;
-	int m_actualRows;
-	int m_actualCols;
-	int m_prepared;
-	int m_columnOffset; // indexes the "start column" in the datasource. Data will be imported starting from this column.
 	QVector<void*> m_dataContainer; // pointers to the actual data containers
 };
 
 #endif