# Using Slicer plot view signal
**URL:** https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025
**Category:** Development
**Created:** [September 8, 2018, 12:16am UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025 "2018-09-08T00:16:00Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@Mateo\_Lopez](https://discourse.slicer.org/u/Mateo_Lopez)
#### Post date: [September 8, 2018, 12:16am UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025/1 "2018-09-08T00:16:00Z")
Hello,
I am not used to coding python scripts for Slicer and I am wondering how I can use the dataSelected signal provided by PlotViews.
I am creating some plots to visualize PCA data and I would like to detect when a point is selected on my projection plot.
I tried the following code to generate all the nodes I need and tried to create a qMRMLPlotView object to connect the dataSelected signal but it doesn’t seem to be working.
Do you know a proper way to use this signal?
code:
```
def generate2DVisualisationNodes(self):
#clean previously created nodes
self.delete2DVisualisationNodes()
#generate PlotChartNodes to visualize the variance plot and the Projection plot
variancePlotChartNode = self.generateVariancePlot()
projectionPlotChartNode = self.generateProjectionPlot()
# Switch to a layout that contains a plot view to create a plot widget
layoutManager = slicer.app.layoutManager()
layoutWithPlot = slicer.modules.plots.logic().GetLayoutWithPlot(layoutManager.layout)
layoutManager.setLayout(layoutWithPlot)
# Select chart in plot view
plotWidget = layoutManager.plotWidget(0)
plotViewNode = plotWidget.mrmlPlotViewNode()
plotViewNode.SetPlotChartNodeID(projectionPlotChartNode.GetID())
plotViewNode.SetPlotChartNodeID(variancePlotChartNode.GetID())
plotView = slicer.qMRMLPlotView()
plotView.setMRMLPlotViewNode(plotViewNode)
plotView.connect("dataSelected(vtkStringArray, vtkCollection)", self.onDataSelected)
def generateProjectionPlot(self):
projectionTableNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLTableNode","PCA projection table")
table = projectionTableNode.GetTable()
pc1=vtk.vtkFloatArray()
pc2=vtk.vtkFloatArray()
pc1.SetName("pc1")
pc2.SetName("pc2")
table.AddColumn(pc1)
table.AddColumn(pc2)
#Projection plot serie
projectionPlotSeries = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLPlotSeriesNode", "PCA projection")
projectionPlotSeries.SetAndObserveTableNodeID(projectionTableNode.GetID())
projectionPlotSeries.SetXColumnName("pc1")
projectionPlotSeries.SetYColumnName("pc2")
projectionPlotSeries.SetPlotType(slicer.vtkMRMLPlotSeriesNode.PlotTypeScatter)
projectionPlotSeries.SetLineStyle(slicer.vtkMRMLPlotSeriesNode.LineStyleNone)
projectionPlotSeries.SetUniqueColor()
# Create projection plot chart node
projectionPlotChartNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLPlotChartNode","PCA projection plot chart")
projectionPlotChartNode.AddAndObservePlotSeriesNodeID(projectionPlotSeries.GetID())
projectionPlotChartNode.SetTitle('Population projection')
projectionPlotChartNode.SetXAxisTitle('pc1')
projectionPlotChartNode.SetYAxisTitle('pc2')
return projectionPlotChartNode
```
Thank you!
Mateo
---
### Author:  [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [September 8, 2018, 2:01am UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025/2 "2018-09-08T02:01:01Z")
The correct syntax of creating the connection is:
```
plotView.connect("dataSelected(vtkStringArray*, vtkCollection*)", self.onDataSelected)
```
If you try to connect a non-existing signal then you can see an error message in the application log.
---
### Author:  [@Mateo\_Lopez](https://discourse.slicer.org/u/Mateo_Lopez)
#### Post date: [September 8, 2018, 9:51pm UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025/3 "2018-09-08T21:51:27Z")
Thank you for this quick answer, I have no more error in the application log but it’s still not working. Am I connecting the signal of the right object?
I wonder if there is a way to directly get the qMRMLPlotView object of Slicer instead of creating one.
---
### Author:  [@Mateo\_Lopez](https://discourse.slicer.org/u/Mateo_Lopez)
#### Post date: [September 8, 2018, 10:25pm UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025/4 "2018-09-08T22:25:40Z")
Now it’s working, I was not creating the qMRMLPlotView object the right way. using the plotWidget object to create it solved my problem.
Thank you for your help!
here is the code that worked for me
```
plotWidget = layoutManager.plotWidget(0)
plotViewNode = plotWidget.mrmlPlotViewNode()
plotViewNode.SetPlotChartNodeID(projectionPlotChartNode.GetID())
plotViewNode.SetPlotChartNodeID(variancePlotChartNode.GetID())
plotView = plotWidget.plotView()
plotView.connect("dataSelected(vtkStringArray*, vtkCollection*)", self.onDataSelected)
```
---
### Author:  [@Davide\_Punzo](https://discourse.slicer.org/u/Davide_Punzo)
#### Post date: [September 10, 2018, 9:34am UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025/5 "2018-09-10T09:34:14Z")
Hi Mateo,
It will be great if you can add the example as documentation here:
[https://www.slicer.org/wiki/Documentation/Nightly/Developers/Plots](https://www.slicer.org/wiki/Documentation/Nightly/Developers/Plots)
in the **Signal** section
or/and
[https://www.slicer.org/wiki/Documentation/Nightly/ScriptRepository](https://www.slicer.org/wiki/Documentation/Nightly/ScriptRepository)
Thanks in advance,
Cheers,
Davide.
---
### Author:  [@Mateo\_Lopez](https://discourse.slicer.org/u/Mateo_Lopez)
#### Post date: [September 10, 2018, 2:03pm UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025/6 "2018-09-10T14:03:56Z")
Hi Davide,
Unfortunately, I don’t have the rights to modify the Slicer wiki, I will try to send a request to do so
Cheers,
Mateo
---
### Author:  [@Davide\_Punzo](https://discourse.slicer.org/u/Davide_Punzo)
#### Post date: [September 10, 2018, 10:39pm UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025/7 "2018-09-10T22:39:23Z")
Ok thanks! In the case you don’t manage to get the rights, I can copy and paste the example script (if for you it is ok).
---
### Author:  [@Mateo\_Lopez](https://discourse.slicer.org/u/Mateo_Lopez)
#### Post date: [September 11, 2018, 4:27pm UTC](https://discourse.slicer.org/t/using-slicer-plot-view-signal/4025/8 "2018-09-11T16:27:28Z")
Sure, I have no problem with that, I let you do it, I think it will be easier like this.
Also, I find out that it could be useful to disconnect the signal before connecting it, I had Slicer crashes while reloading the module and using the signal.