question on nuswide dataset

Hi authors, in the paper, you mention that nuswide "use the subset of 195,834 images that are associated with the 21 most frequent concepts", but i saw vector with size of 81 in "data/nuswide_81/train.txt", may I know where do you filter the data? Or you are just using the data specified in those txt files? How about data without labels (vector with all 0s)?