Replacing missing values from a numeric variable with -1

theWay

I don't understand the purpose behind that. What if I'm prepping the data to do a logistic regression? How is the -1 going to affect things?

MartinLiebig

Hi,

I am not sure for a logistic regression. But there are sometimes cases where you e.g. a algorithm did not work and did not give you any result. In this case people sometimes replace with "magic" values. e.g. -1 or -42. Thats one of the common things to do.
Be careful using it. For some algorithms this -1 makes things wired. E.g. k-NN.

~Martin