In what case the value for categorical feature will be `0`?

[huangbiubiu]

As mentioned in README.md https://github.com/shichence/AutoInt/blob/master/README.md#input-format:

• train_x: matrix with shape (num_sample, num_field). train_x[s][t] is the feature value of feature field t of sample s in the dataset. The default value for categorical feature is 1.

In what case the categorical feature will NOT be 1? Thanks!