Why do the number of lines double when poi-tl draws a double Y-axis line chart?

Investigation and solution to the problem of double the number of polylines when drawing a double Y-axis line chart of poi-tl library

When creating a double Y-axis line chart using the poi-tl library, the number of lines doubled: only two lines are added to the code, but the rendering results show four lines, overlapping the two. This problem is not a data error, the data structure is still correct during debugging.

Troubleshooting: After replacing the combo chart in the Word template with a single Y-axis line chart, the problem disappears, indicating that the problem is related to the way Poi-tl handles the double Y-axis combined chart.

Problem analysis: The code uses Charts.ofComboSeries() to create a chart and add two polyline data with addLineSeries() (corresponding to bnYear "年" and qnYear "年" respectively). When Charts.ofComboSeries() processes double Y axis, it may implicitly create two polylines for each data, corresponding to the main Y axis and the secondary Y axis, resulting in the final four polylines. The key is that the code does not specify the correspondence between the data and the Y axis.

Solution: You need to specify which Y axis corresponds to each polyline. This may require:

1. Check the poi-tl document: Check the official poi-tl document in detail, find the behavior description of Charts.ofComboSeries() method in dual Y-axis scenarios, and how to specify the mapping relationship between the data and the Y-axis. addLineSeries() method may have parameters that can be used to specify the Y axis.

2. Try other APIs: Explore other API functions provided by poi-tl to more granularly control chart drawing and clarify the association of data with coordinate axes.

3. Consider alternatives: Consider creating two single Y-axis charts separately and then group them together using the combined charting features provided by poi-tl to achieve the desired effect. This method is more direct and easier to control the data on each Y axis.

In short, the core of solving the problem lies in understanding and correctly using the API about double Y-axis chart drawing in the poi-tl library to clarify the correspondence between the data and the Y-axis. It is recommended to read the documentation carefully and try different ways to solve this problem.

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