Insert independent curve into scatter chart

[mholz]

Hey guys,

I'm struggling with a problem I have using the google chart API.

Right now, I'm using a scatter chart to display several points on a 2D-plane and make heavy use of features like annotations and animations. This works perfectly fine.

My problem is: I want to add a curve into the same chart that is completely independent from these points. What I mean with this is that this curve is based on a different data table, so the data points defining the curve have nothing to do with the points shown in the scatter chart except for the fact that they are defined on the same axes. We could e.g. have 100 points in the scatter chart and 3 very different points that define the curve.

Here is a picture of something similar, referring to the single points and this square-root-like curve:

https://upload.wikimedia.org/wikipedia/commons/e/e1/Markowitz_frontier.jpg

Actually, this leads me to two questions:

1. Is it possible to add this curve, basically defined by 3 points and interpolated by a quadratic function?
2. Is it possible to make this curve somewhat shallow, so that it is ignored when the API resizes the picture to the points in the scatter plot?

I hope my questions is not too confusing ;-)

Thanks!

[Daniel LaLiberte]

Short answer is, yes, you can combine scatter and line charts, but only for the classic (non-material) charts.  Look into the combo chart.   https://developers.google.com/chart/interactive/docs/gallery/combochart

You can use null values in any column where you don't have points or lines

Lines can connect arbitrary points.

You might be able to use the polynomial trendline to interpolate 3 points with degree 2 (for quadratic).  You would have to flip the orientation to 'vertical' to get the domain on the vertical axis, however.

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Daniel LaLiberte

dlaliberte@Google.com   5CC, Cambridge MA

[mholz]

Thank you Daniel, this works perfectly! The key point was that I should use null values. Defining a polynomial trendline of degree 2 then does the job.

Two questions remain from my side:

1. As before: Is it possible to make these 3 points shallow/invisible/massless (I cannot find the correct word) so that they are not considered when it comes to resizing the axes? I really rely on the default feature of Google graph that it 'zooms' into a smaller region that contains all the data points. The quadratic part shall only be seen if it is in this viewing area by accident.
2. Is it possible define a range for trendlines? Right now, I get a proper parabola, flipped by 90°. I'm actually only interested in the left part of the parabola / the positive part of the square root function.

Thanks again for the great help!

Am Montag, 22. Januar 2018 15:25:11 UTC+1 schrieb Daniel LaLiberte:

Short answer is, yes, you can combine scatter and line charts, but only for the classic (non-material) charts.  Look into the combo chart.   https://developers.google.com/chart/interactive/docs/gallery/combochart

You can use null values in any column where you don't have points or lines

Lines can connect arbitrary points.

You might be able to use the polynomial trendline to interpolate 3 points with degree 2 (for quadratic).  You would have to flip the orientation to 'vertical' to get the domain on the vertical axis, however.

On Mon, Jan 22, 2018 at 5:08 AM, mholz <m.ho...@gmail.com> wrote:

Hey guys,

I'm struggling with a problem I have using the google chart API.

Right now, I'm using a scatter chart to display several points on a 2D-plane and make heavy use of features like annotations and animations. This works perfectly fine.

My problem is: I want to add a curve into the same chart that is completely independent from these points. What I mean with this is that this curve is based on a different data table, so the data points defining the curve have nothing to do with the points shown in the scatter chart except for the fact that they are defined on the same axes. We could e.g. have 100 points in the scatter chart and 3 very different points that define the curve.

Here is a picture of something similar, referring to the single points and this square-root-like curve:

https://upload.wikimedia.org/wikipedia/commons/e/e1/Markowitz_frontier.jpg

Actually, this leads me to two questions:

1. Is it possible to add this curve, basically defined by 3 points and interpolated by a quadratic function?
2. Is it possible to make this curve somewhat shallow, so that it is ignored when the API resizes the picture to the points in the scatter plot?

I hope my questions is not too confusing ;-)

Thanks!

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Daniel LaLiberte

dlali...@Google.com   5CC, Cambridge MA

[Daniel LaLiberte]

There is currently no way to use the explorer mode selectively on some vertical axes and not all, but that would probably be the solution you need.  You can limit to horizontal only or vertical only.

Otherwise, you will have to rescale your data points to have it produce the desired parabola, and to do that while zooming will be difficult, though it is possible.  It might be easier to use an overlay.

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Daniel LaLiberte

dlali...@Google.com   5CC, Cambridge MA

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Daniel LaLiberte

dlaliberte@Google.com   5CC, Cambridge MA