Fairly picking a line out of a text file isn't constant time. It depends on the length of the file. You can pick a random byte offset and find the next line bu

Fairly picking a line out of a text file isn't constant time. It depends on the length of the file. You can pick a random byte offset and find the next line but this prefers longer lines. Preprocessing to basically make a table of line offsets allows constant time access. Probably mattered more when storage was slower.