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  Why does rabies cause hydrophobia? 
  
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Has hydrophobia been found outside of rabies?

I have only seen it being mentioned as a symptom of rabies.


Question: R biglm predict searching for dependent variable
Answer: The reason it is looking for the dependent variable is that the predict method uses a call to model.frame from the stats package, and that function requires all the variables to be present in the new data. This is indicated on the model.frame help page without explanation for the motivation behind it. 

All you actually need to do about this is create a variable in your new data that has the same name as the dependent variable, then fill it with zeroes (or any non-missing value). So it should work if you run this:

df1$price &lt;- 0
pred1 &lt;- predict(a, df1)