Multiple classes in a list, ImageDataBunch.from_lists(data_path, fn_paths, labels) only get one?

Part 1 (2019)
1

fn_paths = list(df[‘path’])
labels = list(df[‘diagnosis’].map(lambda x: str(x)))
data = ImageDataBunch.from_lists(data_path, fn_paths, labels)
data.classes
[‘2’]

I get a df containing filename path and classes, and I wanna use: ImageDataBunch.from_lists() to get my data. My label has 4 classes, but data.classes turned out to be only 1 class.
Why?