5 ms·

NaN does not mean "I am not a number”

21 points by thinker 12y ago

PhasmaFelis 12y ago
I love the folks getting all snarky and superior at the guy who was foolish enough to suggest that "Not a Number" should not be a number. There's probably some cutting insight into programmer culture here somewhere.
- deleted 12y ago
  [deleted]
xupybd 12y ago
This may be correct, but why name it NaN if its a number. I thought we were meant to write readable code. Poor naming like this in the specs really does not help.
- dragonwriter 12y ago
  > This may be correct, but why name it NaN if its a number. It is definitively not a number in the usual, mathematical sense -- hence the name, which comes from IEEE 754. However, the isNumber function doesn't really check if things are numbers, it checks if they are of the Number type, which, potentially confusingly, includes things which are not numbers, including the accurately named value Not-a-Number (NaN).
  - xupybd 12y ago
    So it's Not-a-Number but isNumber returns true? That would imply then that isNumber is named incorrectly. So perhaps isNumber should read isNumericType? Most of the time I want to test, is this a number I can use in a normal mathematical sense. As in, can I use it in subtraction, multiplication etc. I know now that I should use isFinite and isNumber, but wouldn't it be nice to have just one well named function for this?
    - dragonwriter 12y ago
      > So it's Not-a-Number but isNumber returns true? NaN is not a number (the concept) but it is a Number (the type). > That would imply then that isNumber is named incorrectly. Arguably, it is Number (the type) that is named incorrectly (a type called Number that includes a value called Not-a-Number seems problematic.) Maybe "Number" should be called "MaybeNumber". And, perhaps more importantly, the fact that JS doesn't have a convenient type membership operator for primitive types is problematic, as if there was a convenient parallel to "instanceOf" for primitive types -- or if "instanceOf" just worked for them -- then libraries wouldn't need to provide something like what underscores isNumber does at all, and then any isNumber function would probably test "is the argument a number" rather than "is the argument a Number".
      - xupybd 12y ago
        We just need a way to indicate if the method is checking the type or the value.
    - cypher543 12y ago
      It's consistent with the names of other type-checking functions. isNumber checks if a value is an instance of the Number class just like isDate checks if a value is an instance of the Date class. If it were isNumericType, they'd get questions about why the function doesn't follow the existing naming convention. The only reason this is confusing for people is because they aren't familiar with IEEE 754 floating-point numbers and their representations. But since floats are used in almost every programming language, it's something that any programmer should be familiar with. Once they learn exactly what NaN means in that context, then the confusion should disappear.
      - xupybd 12y ago
        I really dislike this sort of reasoning. That its only confusing because you don't know enough. It's possible to word things in ways that are easy to learn and lead you to an understanding of the underlying mechanics. Its confusing because NaN explicitly states not a number. Then the function explicitly states is number. However the two are in very different contexts, yet this is not communicated when using them. It's intuitive to think of a date as a class and there for the context is implicit in isDate. I don't think this is the case for isNumber. I think this is less about people understanding floating-point numbers more about understanding that a function starting with is implies some form of type checking.
personjerry 12y ago
tl;dr: Guy suggests isNumber(NaN) should be false. But it's true because NaN is part of floating points as defined by IEEE. My own interpretation? While programmers shouldn't care so much about this particular kind of semantics (instead they should understand the theory behind floats and never have to run into this issue) it might be better just to call NaNs something else, like "undefined number" or something.
- dragonwriter 12y ago
  > My own interpretation? While programmers shouldn't care so much about this particular kind of semantics (instead they should understand the theory behind floats and never have to run into this issue) it might be better just to call NaNs something else, like "undefined number" or something. Or, better, call the JavaScript type that represents IEEE-754 Binary64 format -- which includes the union of three sets (finite numbers in a given range, two infinite numbers, and two kinds of Not-a-Number values) something other than "Number".
- wlievens 12y ago
  As dragonwriter has remarked above, the type "Number" includes stuff that isn't a number. That's a bit absurd, it's like having a value "Red" for a "Color" type. The type should obviously have been called Float or some variant of that, and the type identification function isFloat.
derefr 12y ago
Isn't this what type systems are supposed to be for? 1.0 / 1.0 => Just 1.0 0.0 / 0.0 => Nothing
fpaboim 12y ago
This discussion is ridiculous. NaN should obviously return true of isNumber, and probably just indicates you did something funky with your numbers and they exploded. They're still numbers, you're the one who's at fault (I never really saw NaN come by on purpose...). It's just that computers can't really represent some numbers and when that happens you get NaN and as much as you want languages to read as english or be perfect abstractions sometimes practical implementations details end up surfacing and theres nothing you can do.
- twiceaday 12y ago
  1%0 is not found on the number line. It's not a number.
- wlievens 12y ago
  > I never really saw NaN come by on purpose We use NaN for masking in image processing, for instance for filtering out defective pixels. If a pixel has value NaN, it is ignored across the board.
- xupybd 12y ago
  But there is something we can do. We can make the context clear and resolve this.

21 points by thinker 12y ago

I love the folks getting all snarky and superior at the guy who was foolish enough to suggest that "Not a Number" should not be a number. There's probably some cutting insight into programmer culture here somewhere.

deleted 12y ago
[deleted]

xupybd 12y ago

This may be correct, but why name it NaN if its a number. I thought we were meant to write readable code. Poor naming like this in the specs really does not help.

dragonwriter 12y ago
> This may be correct, but why name it NaN if its a number. It is definitively not a number in the usual, mathematical sense -- hence the name, which comes from IEEE 754. However, the isNumber function doesn't really check if things are numbers, it checks if they are of the Number type, which, potentially confusingly, includes things which are not numbers, including the accurately named value Not-a-Number (NaN).
- xupybd 12y ago
  So it's Not-a-Number but isNumber returns true? That would imply then that isNumber is named incorrectly. So perhaps isNumber should read isNumericType? Most of the time I want to test, is this a number I can use in a normal mathematical sense. As in, can I use it in subtraction, multiplication etc. I know now that I should use isFinite and isNumber, but wouldn't it be nice to have just one well named function for this?
  - dragonwriter 12y ago
    > So it's Not-a-Number but isNumber returns true? NaN is not a number (the concept) but it is a Number (the type). > That would imply then that isNumber is named incorrectly. Arguably, it is Number (the type) that is named incorrectly (a type called Number that includes a value called Not-a-Number seems problematic.) Maybe "Number" should be called "MaybeNumber". And, perhaps more importantly, the fact that JS doesn't have a convenient type membership operator for primitive types is problematic, as if there was a convenient parallel to "instanceOf" for primitive types -- or if "instanceOf" just worked for them -- then libraries wouldn't need to provide something like what underscores isNumber does at all, and then any isNumber function would probably test "is the argument a number" rather than "is the argument a Number".
    - xupybd 12y ago
      We just need a way to indicate if the method is checking the type or the value.
  - cypher543 12y ago
    It's consistent with the names of other type-checking functions. isNumber checks if a value is an instance of the Number class just like isDate checks if a value is an instance of the Date class. If it were isNumericType, they'd get questions about why the function doesn't follow the existing naming convention. The only reason this is confusing for people is because they aren't familiar with IEEE 754 floating-point numbers and their representations. But since floats are used in almost every programming language, it's something that any programmer should be familiar with. Once they learn exactly what NaN means in that context, then the confusion should disappear.
    - xupybd 12y ago
      I really dislike this sort of reasoning. That its only confusing because you don't know enough. It's possible to word things in ways that are easy to learn and lead you to an understanding of the underlying mechanics. Its confusing because NaN explicitly states not a number. Then the function explicitly states is number. However the two are in very different contexts, yet this is not communicated when using them. It's intuitive to think of a date as a class and there for the context is implicit in isDate. I don't think this is the case for isNumber. I think this is less about people understanding floating-point numbers more about understanding that a function starting with is implies some form of type checking.

personjerry 12y ago

tl;dr: Guy suggests isNumber(NaN) should be false. But it's true because NaN is part of floating points as defined by IEEE. My own interpretation? While programmers shouldn't care so much about this particular kind of semantics (instead they should understand the theory behind floats and never have to run into this issue) it might be better just to call NaNs something else, like "undefined number" or something.

dragonwriter 12y ago
> My own interpretation? While programmers shouldn't care so much about this particular kind of semantics (instead they should understand the theory behind floats and never have to run into this issue) it might be better just to call NaNs something else, like "undefined number" or something. Or, better, call the JavaScript type that represents IEEE-754 Binary64 format -- which includes the union of three sets (finite numbers in a given range, two infinite numbers, and two kinds of Not-a-Number values) something other than "Number".
wlievens 12y ago
As dragonwriter has remarked above, the type "Number" includes stuff that isn't a number. That's a bit absurd, it's like having a value "Red" for a "Color" type. The type should obviously have been called Float or some variant of that, and the type identification function isFloat.

derefr 12y ago

Isn't this what type systems are supposed to be for? 1.0 / 1.0 => Just 1.0 0.0 / 0.0 => Nothing

fpaboim 12y ago

This discussion is ridiculous. NaN should obviously return true of isNumber, and probably just indicates you did something funky with your numbers and they exploded. They're still numbers, you're the one who's at fault (I never really saw NaN come by on purpose...). It's just that computers can't really represent some numbers and when that happens you get NaN and as much as you want languages to read as english or be perfect abstractions sometimes practical implementations details end up surfacing and theres nothing you can do.

twiceaday 12y ago
1%0 is not found on the number line. It's not a number.
wlievens 12y ago
> I never really saw NaN come by on purpose We use NaN for masking in image processing, for instance for filtering out defective pixels. If a pixel has value NaN, it is ignored across the board.
xupybd 12y ago
But there is something we can do. We can make the context clear and resolve this.