How to specify a Spotfire regression model with no intercept.
Article ID: KB0073559
Updated On:
| Products | Versions |
|---|---|
| Spotfire Analyst | All |
| Spotfire Enterprise Runtime for R | All |
Description
How to specify a Spotfire regression model with no intercept.
Issue/Introduction
You can specify a Spotfire linear regression model with no intercept by manually editing the regression formula that is sent to Spotfire's TIBCO Enterprise Runtime for R (TERR) engine for processing.
Environment
All supported environments
Resolution
In the text field named "Formula expression (column names quoted with backticks)" at the bottom of Spotfire's "Tools > Regression Modeling" dialog, you can specify a zero intercept by typing -1 at the end of the formula.
For example, if you have used the dialog's point-and-click options to define the following formula expression:
`Fuel` ~ `Weight`
you can edit it to read as follows to specify a zero intercept ("no intercept") in the regression model:
`Fuel` ~ `Weight` - 1
With this change, the resulting model's "Coefficients" component will list a coefficient for the Weight column, but it will not list an intercept because the formula has defined the model's y-intercept to be zero. The regression model is generated using a Spotfire data function that sends the data and a script to TIBCO Spotfire Enterprise Runtime for R (TERR) for processing.
Important Note: The syntax for this method uses the number 1, as in the following example:
`Fuel` ~ `Weight` - 1
It will fail if you try to use a lower-case "l" (that is, the lower-case version of the letter "L"), as in the following example:
`Fuel` ~ `Weight` - l
If you try to use a lower-case "l", it will look for a TERR object named 'l'. If there is no such object, it will throw the following error:
-----------
TIBCO Enterprise Runtime for R returned an error
The data function 'MyModel' could not be executed.
Error in eval(attr(formula, "variables"), envir = data, enclos = encl : object 'l' not found
-----------
For example, if you have used the dialog's point-and-click options to define the following formula expression:
`Fuel` ~ `Weight`
you can edit it to read as follows to specify a zero intercept ("no intercept") in the regression model:
`Fuel` ~ `Weight` - 1
With this change, the resulting model's "Coefficients" component will list a coefficient for the Weight column, but it will not list an intercept because the formula has defined the model's y-intercept to be zero. The regression model is generated using a Spotfire data function that sends the data and a script to TIBCO Spotfire Enterprise Runtime for R (TERR) for processing.
Important Note: The syntax for this method uses the number 1, as in the following example:
`Fuel` ~ `Weight` - 1
It will fail if you try to use a lower-case "l" (that is, the lower-case version of the letter "L"), as in the following example:
`Fuel` ~ `Weight` - l
If you try to use a lower-case "l", it will look for a TERR object named 'l'. If there is no such object, it will throw the following error:
-----------
TIBCO Enterprise Runtime for R returned an error
The data function 'MyModel' could not be executed.
Error in eval(attr(formula, "variables"), envir = data, enclos = encl : object 'l' not found
-----------
Additional Information
For more information you can open a TERR Console session (by selecting "Tools > TERR Tools > Launch TERR Console" from the Spotfire desktop client's main menu), then issue the following commands to open the relevant TERR help files in a web browser:
?lm
?formula.object
The following item among the examples in the "formula.object" help file illustrates how this would be done in a TERR console session:
# no intercept
lm(Fuel ~ Weight - 1, data=fuel.frame)
?lm
?formula.object
The following item among the examples in the "formula.object" help file illustrates how this would be done in a TERR console session:
# no intercept
lm(Fuel ~ Weight - 1, data=fuel.frame)
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