Chris Angelico wrote: > On Fri, Jul 15, 2011 at 3:28 PM, Steven D'Aprano > <steve+comp.lang.pyt...@pearwood.info> wrote: >> My question is, should I accept None as the missing value, or a dedicated >> singleton? >> >> In favour of None: it's already there, no extra code required. People may >> expect it to work. >> >> Against None: it's too easy to mistakenly add None to a data set by >> mistake, because functions return None by default. > > I guess the question is: Why are the missing values there? If they're > there because some function returned None because it didn't have a > value to return, and therefore it's a missing value, then using None > as "missing" would make a lot of sense. But if it's a more explicit > concept of "here's a table of values, and the user said that this one > doesn't exist", it'd be better to have an explicit MISSING. (Which I > assume would be exposed as yourmodule.MISSING or something.)
In general, you have missing values in statistics because somebody wouldn't answer a question, and the Ethics Committee frowns on researchers torturing their subjects to get information. They make you fill out forms. Seriously, missing data is just missing. Unknown. Lost. Not available. Like: Name Age Income Years of schooling ============================================== Bill 42 150,000 16 Susan 23 39,000 14 Karen unknown 89,000 15 Bob 31 0 7 George 79 12,000 unknown Sally 17 19,000 5 Fred 66 unknown 11 One might still like to calculate the average age as 43. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
