Deneb Example - Regression

[Greg]

Deneb/Vega-Lite can be used to create regression analyses in Power BI. Vega-Lite has 6 regression algorithms built-in: linear, logarithmic, exponential, power, quadratic, and polynomial. The example visual presented herein consists of a scatter chart using movie ratings overlayed with a regression line and an R-squared statistic.

This example illustrates a number of Deneb/Vega-Lite features, including:

0 - General:

• use of a “params” block to create a radio-button screen widget for selecting the regression algorithm
• use of a “layer” block consisting of 3 sections: scatter chart, regression line, and r-squared statistic.

1 - Scatter Chart:

• use of a “point” mark to display IMDB rating vs. Rotten Tomatoes rating (the raw data)
  • both the X and Y axes use custom axis tick counts (10)
  • custom tooltip with title, release year, release date, IMDB rating, and Rotten Tomatoes rating

2 - Regression Line:

• use of a “transform” block to apply the (selected) regression algorithm to the raw data
  • thanks to Davide Bacci for sharing his insight on using Vega code within Vega-Lite in his recent (July 2023) response to a Stack Overflow question about using parameter values in regression calculations https://stackoverflow.com/questions/76709441/in-vega-lite-deneb-how-do-i-apply-a-parameter-list-of-regression-types-to-a-ca
• use of a “line” mark for the regression line (thick; red)

3 - Regression Statistic:

• use of a “transform” block to apply the (selected) regression algorithm to the raw data and calculate the r-squared statistic
• use of a “text” mark located at the center of the visual (width/2; height/2) to display the r-squared statistic

The intent of this example is not to provide a finished visual, but rather to serve as a starting point for further custom visual development.

Also included is the sample PBIX using the movies JSON file provided on the Vaga-Lite examples website.

This example is provided as-is for information purposes only, and its use is solely at the discretion of the end user; no responsibility is assumed by the author.

Greg
Deneb Examples - Regression.pbix (1.5 MB)

[Greg]

marking as solved

[fabrice.aunez]

Thanks a lot Greg, Very interesting
If I may ask two questions :
1/ is signal the key to force the data transformation following to a change of selection made by user ? In fact, I have some difficulties withi this signal
2/ I do not see the dataset following this transformation (nothing added ?). Therefore I do not understand on what field the line is drawn. Because you have set a regression based on two fields, you just need to recode these fiels to get it ?

Fabrice

[Greg]

Hi @fabrice.aunez.

1 - Yes, once the user has selected a regression method, the signal is used to reference it in the transform; AFAIK, you can’t do this in Vega-Lite, but Davide Bacci’s method (see above) of using Vega within Vega-Lite seems to work great:

  "transform": [
    {
      "regression": "IMDB Rating",
      "on": "Rotten Tomatoes Rating",
      "method": {
        "signal": "_regression_keyword"
      }
    }
  ],

2 - I’m not sure exactly, as Vega-Lite does the regression calculations internally, but think it is the REGRESSION_LINE_marks dataset; I certainly didn’t add anything

Hope this helps.
Greg