Manage Chart Data Labels in Presentations Using Python
Introduction
Data labels on a chart show details about the chart data series or individual data points. They allow readers to quickly identify data series, and they also make charts easier to understand.
Set Data Precision in Chart Data Labels
This Python code shows you how to set the data precision in a chart data label:
import jpype
import asposeslides
if not jpype.isJVMStarted():
jpype.startJVM()
from asposeslides.api import ChartType, Presentation, SaveFormat
presentation = Presentation()
try:
chart = presentation.getSlides().get_Item(0).getShapes().addChart(ChartType.Line, 50, 50, 450, 300)
chart.setDataTable(True)
chart.getChartData().getSeries().get_Item(0).setNumberFormatOfValues("#,##0.00")
presentation.save("output.pptx", SaveFormat.Pptx)
finally:
presentation.dispose()
Display Percentage as Labels
Aspose.Slides for Python via Java allows you to set percentage labels on displayed charts. This Python code demonstrates the operation:
import jpype
import asposeslides
if not jpype.isJVMStarted():
jpype.startJVM()
from asposeslides.api import ChartType, Portion, Presentation, SaveFormat
presentation = Presentation()
try:
slide = presentation.getSlides().get_Item(0)
chart = slide.getShapes().addChart(ChartType.StackedColumn, 20, 20, 400, 400)
chart_series = chart.getChartData().getSeries()
category_totals = [0.0] * chart.getChartData().getCategories().size()
for category_index in range(len(category_totals)):
for series_index in range(chart_series.size()):
data_point = chart_series.get_Item(series_index).getDataPoints().get_Item(category_index)
category_totals[category_index] += float(data_point.getValue().getData())
for series_index in range(chart_series.size()):
series = chart_series.get_Item(series_index)
series.getLabels().getDefaultDataLabelFormat().setShowLegendKey(False)
for point_index in range(series.getDataPoints().size()):
data_point = series.getDataPoints().get_Item(point_index)
label = data_point.getLabel()
if category_totals[point_index] == 0:
print(f"Cannot calculate a percentage for category {point_index}: the total is zero.")
continue
point_percentage = float(data_point.getValue().getData()) / category_totals[point_index] * 100
portion = Portion()
portion.setText(f"{point_percentage:.2f} %")
portion.getPortionFormat().setFontHeight(8)
label.getTextFrameForOverriding().setText("")
paragraph = label.getTextFrameForOverriding().getParagraphs().get_Item(0)
paragraph.getPortions().add(portion)
label_format = label.getDataLabelFormat()
label_format.setShowSeriesName(False)
label_format.setShowPercentage(False)
label_format.setShowLegendKey(False)
label_format.setShowCategoryName(False)
label_format.setShowBubbleSize(False)
presentation.save("output.pptx", SaveFormat.Pptx)
finally:
presentation.dispose()
Set Percentage Sign with Chart Data Labels
This Python code shows you how to set the percentage sign for a chart data label:
import jpype
import asposeslides
if not jpype.isJVMStarted():
jpype.startJVM()
from asposeslides.api import ChartType, FillType, Presentation, SaveFormat
Color = jpype.JClass("java.awt.Color")
presentation = Presentation()
try:
slide = presentation.getSlides().get_Item(0)
chart = slide.getShapes().addChart(ChartType.PercentsStackedColumn, 20, 20, 500, 400)
chart.getAxes().getVerticalAxis().setNumberFormatLinkedToSource(False)
chart.getAxes().getVerticalAxis().setNumberFormat("0.00%")
chart.getChartData().getSeries().clear()
worksheet_index = 0
workbook = chart.getChartData().getChartDataWorkbook()
# Add the red series.
series_cell = workbook.getCell(worksheet_index, 0, 1, "Reds")
red_series = chart.getChartData().getSeries().add(series_cell, chart.getType())
for row_index, value in enumerate([0.30, 0.50, 0.80, 0.65], start=1):
data_cell = workbook.getCell(worksheet_index, row_index, 1, jpype.JDouble(value))
red_series.getDataPoints().addDataPointForBarSeries(data_cell)
red_series.getFormat().getFill().setFillType(FillType.Solid)
red_series.getFormat().getFill().getSolidFillColor().setColor(Color.RED)
red_label_format = red_series.getLabels().getDefaultDataLabelFormat()
red_label_format.setShowValue(True)
red_label_format.setNumberFormatLinkedToSource(False)
red_label_format.setNumberFormat("0.0%")
red_portion_format = red_label_format.getTextFormat().getPortionFormat()
red_portion_format.setFontHeight(10)
red_portion_format.getFillFormat().setFillType(FillType.Solid)
red_portion_format.getFillFormat().getSolidFillColor().setColor(Color.WHITE)
# Add the blue series.
series_cell = workbook.getCell(worksheet_index, 0, 2, "Blues")
blue_series = chart.getChartData().getSeries().add(series_cell, chart.getType())
for row_index, value in enumerate([0.70, 0.50, 0.20, 0.35], start=1):
data_cell = workbook.getCell(worksheet_index, row_index, 2, jpype.JDouble(value))
blue_series.getDataPoints().addDataPointForBarSeries(data_cell)
blue_series.getFormat().getFill().setFillType(FillType.Solid)
blue_series.getFormat().getFill().getSolidFillColor().setColor(Color.BLUE)
blue_label_format = blue_series.getLabels().getDefaultDataLabelFormat()
blue_label_format.setShowValue(True)
blue_label_format.setNumberFormatLinkedToSource(False)
blue_label_format.setNumberFormat("0.0%")
blue_portion_format = blue_label_format.getTextFormat().getPortionFormat()
blue_portion_format.setFontHeight(10)
blue_portion_format.getFillFormat().setFillType(FillType.Solid)
blue_portion_format.getFillFormat().getSolidFillColor().setColor(Color.WHITE)
presentation.save("SetDataLabelsPercentageSign_out.pptx", SaveFormat.Pptx)
finally:
presentation.dispose()
Set Label Distance from an Axis
This Python code shows you how to set the label distance from a category axis when you are dealing with a chart plotted from axes:
import jpype
import asposeslides
if not jpype.isJVMStarted():
jpype.startJVM()
from asposeslides.api import ChartType, Presentation, SaveFormat
presentation = Presentation()
try:
slide = presentation.getSlides().get_Item(0)
chart = slide.getShapes().addChart(ChartType.ClusteredColumn, 20, 20, 500, 300)
chart.getAxes().getHorizontalAxis().setLabelOffset(500)
presentation.save("output.pptx", SaveFormat.Pptx)
finally:
presentation.dispose()
Adjust Label Location
When you create a chart that does not rely on any axis, such as a pie chart, the chart’s data labels may end up being too close to its edge. In such a case, you have to adjust the location of the data label so that the leader lines get displayed clearly.
This Python code shows you how to adjust the label location on a pie chart:
import jpype
import asposeslides
if not jpype.isJVMStarted():
jpype.startJVM()
from asposeslides.api import ChartType, LegendDataLabelPosition, Presentation, SaveFormat
presentation = Presentation()
try:
chart = presentation.getSlides().get_Item(0).getShapes().addChart(ChartType.Pie, 50, 50, 200, 200)
series = chart.getChartData().getSeries()
label = series.get_Item(0).getLabels().get_Item(0)
label.getDataLabelFormat().setShowValue(True)
label.getDataLabelFormat().setPosition(LegendDataLabelPosition.OutsideEnd)
label.setX(0.71)
label.setY(0.04)
presentation.save("pres.pptx", SaveFormat.Pptx)
finally:
presentation.dispose()
FAQ
How can I prevent data labels from overlapping on dense charts?
Combine automatic label placement, leader lines, and reduced font size; if necessary, hide some fields (for example, the category) or show labels only for extreme/key points.
How can I disable labels only for zero, negative, or empty values?
Filter data points before enabling labels and turn off display for values of 0, negative values, or missing values according to a defined rule.
How can I ensure a consistent label style when exporting to PDF/images?
Explicitly set fonts (family, size) and verify that the font is available on the rendering side to avoid fallback.