Error in eval(predvars, data, env) : object not found.

I am trying to create a prediction, for decision trees. But every time I execute the line below I receive this error. Even though 'tot_proteins' is a column in my dataset. What could be causing this problem?

Prediction1 <- predict(treeFit,newdata=liver.test[-5],type = 'class')

Thank you!

my first thought is that if tot_proteins is the 5th column in liver.test, then you are dropping it

it is the fifth column, but i dont want to drop it. so how do i fix that?

why did you choose to write [-5] ?
why not omit that ?

i have omitted it and now it is working. but I want to create a confusion matrix with it now like this:

confusionMatrix(Prediction1,liver.test$is_patient)

but i receive this error:
Error: data and reference should be factors with the same levels.

what does that mean and how can i fix that ?

I couldnt possible know your factor levels unless you told me...

levels(Prediction1)
levels(liver.test$is_patient)

Hey,
I was able to fix my liver.test$is_patient to not be null. and now it is the same levels as the prediction1. yet it still gives me the same error. any ideas as to why?

Thank you!!