How to use prediction() in formula?

keith

Hi again,

How do you use the predictions of a model in a subsequent FeatureGeneration formula to transform the values?

I've developed a model that predicts the log-odds of an event, but I want to transform it back to a probability so I can plot it on a scale that is more familiar.

e.g.  LinearRegression of y on x, then use Model Applier to get prediction(y)

I can use FeatureGenerator to convert the dependent to a probability:

prob_y = exp(y) / (1+exp(y))       

... which in RM would be written as:

/(exp(y),+(const[1](), exp(y))

However, when I try to do the same thing with the predicted values, which are named by the ModelApplier node as "prediction(y)", the parentheses in the name cause errors:

/(exp(prediction(y)),+(const[1](), exp(prediction(y)))

I've tried it with single or double quotes, without success:

/(exp('prediction(y)'),+(const[1](), exp('prediction(y)'))
/(exp("prediction(y)"),+(const[1](), exp("prediction(y)"))

Is there a way to reference a feature name that contains a special character (like parens), or do you have to rename the feature to something "safer"?

Thanks,
Keith

keith

Following up on my own question...

I renamed the predicted value from "prediction(y)" to "pred_y".  I am then able to use pred_y in mathematical expressions.  However, I can not create "complex" mathematical expressions, only simple ones.

e.g.

I want to be able to do

pred_y_prob    =    /(exp(pred_y), +(exp(pred_y), const[1]()))

However, I get an error when trying to do so.

NullPointerException occured in 1st application of FeatureGeneration
Process failed: operator cannot be executed.  Check the log messages...

But if I break it up into three steps within the FeatureGeneration node, it works:

pred_y_exp      =    exp(pre_y)
pred_y_plus1  =    +(const[1](), pred_y_exp)
pred_y_prob    =      /(pred_y_exp, pred_y_plus1)

The thing that really puzzles me is that my original formulation works if I use the target variable instead of the predicted target variable:

y_prob    =    /(exp(y), +(exp(y), const[1]()))            #  This works!

Any ideas?

Thanks,
Keith