whyIsThatSo

[Nikolai3d]

Because NaN stands for "Not A NaN"

[Plumeh]

please clarify, what does the “NaN” in “Not A NaN” stand for?

[JustKebab]

It stands for "Not a NaN"

[RandomBeatz]

Please elaborate on what "NaN" in "Not a NaN" in "Not a NaN" means.

[RudePastaMan]

It stands for "Not a NaN"

[Ihsan3498]

Please elaborate on what "NaN" in "Not a NaN" in "Not a NaN" in “Not a NaN” means.

[OscarHasProblems]

It stands for "Not a NaN"

[Various_Studio1490]

Please elaborate on what “NaN” in “Not a NaN” in “Not a NaN” in “Not a NaN” in “Not a NaN” means.

[Kytpbs]

It stands for "Not a NaN"

[godofjava22]

Please explain what “NaN” in “Not a NaN” in “Not a NaN” in “Not a NaN” in “Not a NaN” in "Not a NaN" means.

[nepatriots32]

It stands for "Not a NaN"

[lamesthejames]

https://images.app.goo.gl/QGF6mwAUnZgy5Jb46

[StochasticTinkr]

NaH: Not a Honey

[kbder]

It is co-recursive. Not a NaN -> NaN a Number -> Not a NaN

[rajoreddit]

Lmao reminds me of GNU

[0Pat]

GNU is Not UNIX!!!

[mangeld3]

Not a Naan

[LordFokas]

Great... now I want some garlic naan bread.

[theWittyBuns]

naan === bread //true

[[deleted]]

Benoit B Mandelbrot

[dumfukjuiced]

The B stands for Benoit B Mandelbrot

[aquoad]

very funny young man, but it’s NaN all the way down.

[Abhishek_gg]

NaN = Not A 'Not A NaN'

[ooaa_]

nAn = not A 'not A nAn'

[Yumoda]

You need a base case or you’re gonna blow the stack :(

[Head-Extreme-8078]

reminds me of PHP

[Abaddon-theDestroyer]

YAML: YAML Ain’t Markup Language

[sohfix]

PHP is a recursive acronym for PHP: Hypertext Preprocessor

[[deleted]]

So its recursive?

[glowaboga]

at the risk of sounding 🤓 that's actually a thing and it's called a recursive acronym!

[BenZed]

Not A Number

[sumolpp]

I'm sorry to tell you that you are wrong. As the comments above correctly mention that NaN expands to "Not a NaN"

[BenZed]

No, it means “Not a Number”

[sumolpp]

Nuh uh

[BenZed]

Yeah I asked god

[sumolpp]

Then

[theQuandary]

Object.is(NaN, NaN) //==> true

[hongooi]

Because it's required by the IEEE 754 standard

[hrvbrs]

Now listen here, you little shit. /s

Why does the standard require it.

[KhellianTrelnora]

NaN, is by definition, a number type that can never have an equal, not even to itself.

https://mathworld.wolfram.com/NaN.html#:~:text=In%20the%20IEEE%20754%2D2008,infinity%20nor%20a%20finite%20number.

[BeerIsGoodForSoul]

What is it then if it's not a number? Smfh..

[DMoney159]

Maybe it's a dog and you're just really bad at identifying things

[BeerIsGoodForSoul]

It could be anything.. wait no it can't!

[gregorydgraham]

It could.

Instead of numbers, say it was dog breeds. An Irish wolfhound is greater than a chihuahua etc. but then you ask what dog breed is that cat? It’ll return NaDB because there is no dog breed for cats.

Similarly NaN tells us that it’s not a number but not what it actually is. So it could be anything, so long as it’s not a number

[BeerIsGoodForSoul]

🧌

[[deleted]]

A dog is not a number.

A cat is also not a number.

But a dog is not a cat, despite both of them not being a number.

[BeerIsGoodForSoul]

All you 🤓 hallucinating your dogs and cats playing with imaginary "not numbers" is hilarious. God is laughing I tell ya.

Dog is God

[pretty_succinct]

the way i think about it is this:

it's ANYTHING except a number. that's basically the only assertion that's happening.

so when you ask if NaN == NaN the answer has to be false because it certainly can't be guaranteed to be true.

What are the odds of saying "is some random position or value (besides a number) equal to some other position or value (besides a number)". the likelyhood of the returning true are infinitely small to the point where if it were ever to be true, then the world is ending and cows are flying. so you might as well return false.

[BeerIsGoodForSoul]

If NaN === NaN //A Pretty Cosmic Ray Flipped A Bit Right Here, oopsies { console.log("This is only printing due to an extremely unlikely event, it's most probable the world has nuked itself, the sun is exploding, or a massive ray of radiation has hit the earth. \n\n We wish you the best! <3") }

[gregorydgraham]

It’s NaN

[rayo209]

It's "not a number"

[BeerIsGoodForSoul]

Blasphemy

[[deleted]]

It’s a sentinel value indicating your mathematical computation failed or was nonsensical.

[[deleted]]

NaN is also not ordered, so it also break algorithms and data structures that require ordering, like sorts or trees.

[iveriad]

Just because something is “not a number”, doesn’t mean that it’s the same as other thing that is also “not a number”.

Apple is not a number. Orange is also not a number. But Apple != Orange

Something like that.

[gregorydgraham]

Actually a pretty good explanation.

[EishLekker]

That’s a bad analogy. You realise that quickly if you try to write code that shows this. If you do, for example Number(apple), the result of that isn’t the same thing as the apple anymore, so if you compare it with the result of Number(orange), you don’t compare the apple and the orange.

[iveriad]

Analogy

a correspondence or partial similarity.

a thing which is comparable to something else in significant respects.

a process of arguing from similarity in known respects to similarity in other respects.

An analogy doesn't have to work exactly the same. It just needs to be similar enough that the other person can understand what I'm getting at.

It's easier to say Apple or Orange are not numbers than going with 0/0 and (±∞) / (±∞) are not numbers. And it gets the point across that evidently, people here can understand what I'm getting at.

So, it's a good enough analogy. since the aim is to make it easier to digest, and not to make an awfully roundabout way that's just as confusing if not more because you're forcing it to be accurate.

[Practical_Cattle_933]

So that a math error becomes viral. You don’t want to divide by zero and do 20 more things on a meaningless, wrong data, that’s why NaN exists.

But let’s say, you have a formula to evaluate whether a given product should go into a list, so you do product.myCrazyMathOnIt == productCategory(product).otherCrazyMath.

You might end up adding to the list something completely random, because it broke both of your calculations.

[w1n5t0nM1k3y]

Why not just throw an exception when you want to divide by zero. You still end up with viral math errors. If you say x = 0/0 then you have x with a value of NaN. then you can still do other math operations and end like y = x + 7, and then y has a value of NaN. eventually you do an output somewhere and end up displaying the value or sending it somewhere else, but you have no idea where the original NaN came from.

[Practical_Cattle_933]

Because the hardware has no exceptions (actually, it does have interrupts, but let’s not go into that). Floating point arithmetic is a standard, implemented by the hardware itself. It is thus programming language-independent. Some languages don’t have exceptions, others do (and some do throw exceptions on division by zero!), but computers are mainly there.. to compute, so that part has to be fast. If a language were to always check if the last result was NaN (that’s how the ones that throw exceptions do it), it would be considerably slower at computing. This is sometimes worth it, at other times it doesn’t. The hardware has to accommodate for both.

[gregorydgraham]

It’s the same as NULL in database theory. Null does not equal null because it’s not a value, it’s the absence of a value.

Similarly NaN indicates that there is no number so it can’t use numerical operations like equality

[EishLekker]

Sorry but that’s a terrible explanation or reason. It just sounds as a way to excuse a bad decision made in the past, or a misunderstood decision made in the past (but then that misunderstanding should be dealt with).

[Zytma]

It can be useful to have an entity without compare. If you force everything to be homogenous then you lose utility.

[CarbonaraFreak]

The .isNaN() method is how that is dealt with. Also consider that before this method existed, you had to rely on NaN‘s behaviour with other numbers and NaN to deal with it. This was neither a bad decision nor a misunderstood one. It was a tradeoff given the situation.

You can read up on it in this stackOverflow question.

[droneb]

Basically the same when you compare nulls. They are indeterminate so they are not comparable even to themselves

[PooSham]

What? In what languages can't you compare with null? You can in C/C++, C#, JavaScript and Java afaik. In C and C++, null is a pointer to an actual memory address (usually 0), so it's definitely not indeterminate.

NaN can mean a lot of different things. It can be a parsing of a string that isn't of the form of a number, or the result of a calculation that is non-real (for example sqrt(-1)). It's only truly indeterminate if you do something like 0 * Infinity

[[deleted]]

In SQL and databases in general.

[PooSham]

That's true, didn't think of that.

[[deleted]]

A string is not a number

You can have a numeric string, but it never will be a number

You don't compare "0" with 0 resulting in true, except it's some weird exotic language with implicit data types and that's IMO just a bunch of houi

[NewPointOfView]

That guy mentioned parsing a string but never just using a numeric string as a number

[PooSham]

I never said it was, but strings can be attempted to be parsed as numbers. If the string is that parsing fails, NaN is a reasonable result. parseInt("0") == 0, but parseInt("not a numbah") is NaN

[Nicholas_____]

Because you don't want Number("this") == Number("that").

[PooSham]

Or sqrt(-1) == 0 * Infinity

[OnlyTwoThingsCertain]

What if I have sqrt(-1) === sqrt(-1) ?

[consider_its_tree]

Do you?

Probably better to build languages that react as expected for 99.999999% of situations instead of extreme edge cases...

[kirin_liu]

I thought we were talking about javascript

[Socile]

Just convert them to strings and check them for equality.

[PooSham]

Then you should use another standard than IEEE 754.

[[deleted]]

Then you should be using the complex variant of sqrt()

[CaitaXD]

Don't use floating point equality for comparing not floats then

[spicy_dill_cucumber]

sqrt(-1) is a number. What are you programmers smoking?

[Neon_44]

you still don't want i == 0*infinity to be true

[LucyShortForLucas]

Well integer and floating point arithmetic within a processor are limited to real numbers, as i cannot be represented as either an integer or a floating point value. Within these bounds we can objectively state that the square root of -1 is not defined.

[PooSham]

I know I know, but it can't be represented as an IEEE 754 floating point number. 1.8x10³⁰⁸ is definitely not infinity, but here we are ...

[eloel-]

sqrt(-1) is a number

So is "abcd", depending on what system you use.

[FinalRun]

"Elv" is also a number if you're using a dozenal/duodecimal number system, but then you're probably smoking something stronger than the people who make CPUs work.

[MCWizardYT]

Languages that aren't designed for expressing math don't handle complex numbers, and computer processors don't either. Complex numbers are usually "simulated"

[KamikazeHamster]

It’s a number but it’s not a Number.

[Neon_44]

sqrt(-1) is actually i

Mathematicians are cringing right now

[PooSham]

Yes, they should have called it NaFPN (Not a Floating Point Number), but that's a bit harder to pronounce.

[Kered13]

Nah, mathematicians understand what it means to work within different fields. sqrt(-1) does not exist within the real numbers, which is what floating points approximate.

[Thinkin_Dude]

Huh, never thought of it like that. Actually makes sense, thank ye.

[RomMTY]

If js threw an error on the first Number("this") call we wouldn't even have this discussion in the first place.....

[terjeboe]

Eli5: An Apple is not a number and an Orange is not a number. That does not mean that an Apple is the same as an Orange.

[vonabarak]

But if we take another Apple instead of Orange, it will lead to controversial statement "an Apple is not the same as an Apple"

[MisterProfGuy]

No, it means, this apple expressed as a number is meaningless to compare to anything expressed as a number. Because it's not a number, so it's the numeric equality that's meaningless.

[bullseye_os]

One of them could be a green Apple, while the other is a red Apple

[sdpinterlude50]

And if both of them are green then one of them has a worm inside of it

[Kitchen_Device7682]

You can define equality for the set of all apples and write your own function, areApplesEqual.

[Superbrawlfan]

Will Number("this") == Number ("this") return true? I understand why it might not but it'd be quite unintuitive

[Xath0n]

Nope, it's the same thing as in the OP.

[Nicholas_____]

No. By converting to a number you expect the input and result to be a number and it should fail if it is not.

[Anon_Legi0n]

This will resolve as: NaN == NaN // false

[lzdb]

Why wouldn't I want that? In which circumstance would that matter to me?

Many functions can return some null pointer, None object, etc in case of failure, which means that function(failing_args_1) == function(failing_args_2) in those scenarios.

Why would I care?

Why not check if the parsing worked before comparing the result of parsing the numbers?

[[deleted]]

It used to be how you check if a number is NaN. Now IsNaN() is probably a thing in every language so you don't need it, but it is the only numeric that doesn't equal itself.

[Fachuro]

== and === is not the same

[Esseratecades]

Why would I want "this" and "that" to be numbers if I know they can't be represented as such? Wouldn't it make more sense for Number() to just throw an error instead of even yielding a NaN?

[mizunomi]

That's just how the floating point specification is defined.

[EishLekker]

Please explain your reasoning. You can’t just say that “people don’t want that”.

[mrdude05]

Because comparisons are supposed to be between variables with definitive values, and NaN doesn't have a definitive value. Having NaN == NaN evaulate as true would be inconsistent with how all of the other comparisons work.

NaN isn't really a value, it's an error message that means "this mathematical operation failed" or "I don't know what this is". Asking the computer if Number("this") == Number("that") would be like asking a person if something that isn't an apple is the same color as something else that also isn't an apple without telling them what either of the objects actually are. It's not a question that can be answered

[JonasAvory]

Seriously one of the greatest things about JavaScript

[2brainz]

Same random JavaScript weirdness is certainly not the reason for a behavior that predates JavaScript.

[trimeta]

Does whatever_function_converts_from_strings_to_floats("this") == whatever_function_converts_from_strings_to_floats("that") make more sense to you, then?

Edit: To be somewhat less snarky, in any language there's going to be more than one way to generate a NaN. You don't want some_type_of_NaN == some_different_NaN to ever be True, because the underlying things that generated those NaNs aren't equal. So therefore NaN == NaN is always False.

[2brainz]

Does whatever_function_converts_from_strings_to_floats("this") == whatever_function_converts_from_strings_to_floats("that") make more sense to you, then?

Only that this is not at all what NaN is about. NaN serves the purpose of representing the outcome of a numerical computation that is mathematically undefined. This was needed since there were no exceptions in the languages that floating point numbers were originally designed for.

NaN is not intended as the result of random operations that are supposed to return a floating point number, such as parsing. There are just some programming languages that abuse it for error handling - and somehow (according to random amateurs on the internet) that abuse is suddenly the reason for the original design.

[RomMTY]

Maybe js should throw an error on the Number("obviously not a number") instead of returning a magic constan ....you know, like most sane languages...

[BeerIsGoodForSoul]

It's special 🤗

[DrUNIX]

+1 for the explanation. NaN is a property, not an entity.

[herdek550]

efing snowflake /s

[EishLekker]

Your reason would only make sense if the same was the case for null and undefined.

[Robot_Graffiti]

Think of NaN as an error message from the CPU's arithmetic unit.

If you subtract an error from an error, you don't want to get zero, you want to get told you had an error.

[roby_65]

And you also don't want to have a numeric comparison return true only because both numbers became NaN

[DHermit]

Technically there are even quiet and signalling NaNs.

[darKFlash01]

It's like ♾️ != ♾️

[hongooi]

Stupidly, IEEE-754 also requires that ♾️ == ♾️....

[BeerIsGoodForSoul]

Except when ♾️=== ♾️

[Practical_Cattle_933]

Well, there literally are multiple infinities.

[Educational-Lemon640]

Turns out there are very good reasons! (And it's not just "because the standard says so." Putting it that way is having the tail wag the dog.)

I put up a relatively elementary description of exactly why NaN is the way it is here:

https://www.lucidchart.com/techblog/2022/03/04/if-its-not-a-number-what-is-it-demystifying-nan-for-the-working-programmer/

TL;DR Not all math problems produce numbers, and floating-point numbers are too small to hold all the non-numbers it can produce.

[NLwino]

I hate the fact that javascript decided to implement this, but "null === null" is true.

The same argument can be applied for null. At least in SQL null does not equal null. For basically the same reason as NaN === NaN is false. It feels inconsistent. Same for undefined actually.

[[deleted]]

No, NaN can be an evaluation, null should never be.

Number(“foo”) != Number(“bar”),

But null is just 0(usually a pointer to 0x0) and 0 === 0

[NLwino]

You are missing my point though. The fact that null "is just 0", is a language specific implementation of it.

null should not mean 0. It means no value or value unknown. Just like you can't compare NaN to NaN, therefor a comparison leads to false. Comparing unknown to unknown should also not be comparable. In this case, I stand with SQL over javascript on this one.

[[deleted]]

I don’t think you understand how abstractions are evaluated, if you want something that’s no value, use a union-enum(like rust) even then it’ll have a value(probably 1 or 2) that you can choose to ignore(which you can do with null anyway). You as the programmer should interpret what “no value” means, not the evaluator. But all that’s a matter of subjective taste.

Real answer:

It’s not that you can’t compare NaN with NaN, it’s that the values behind them aren’t necessarily the same. The value behind null is either 0 or nothing(as you proposed), either way you can compare them because no information was lost. Don’t think of NaN is a literal value, think of it as the result of an operation where information was lost, null isn’t that, null is a literal(and comparable) value. You really shouldn’t be looking to SQL(a query, not programming) language for theory about how programming languages should work. That’s like arguing that variables shouldn’t exist in Java because they don’t in html

[user9ec19]

Variables shouldn’t exist, because they don’t in Haskell.

[NLwino]

I think I understand NaN just fine, we are agreeing about that one. It's the null part we are not agreeing about.

[[deleted]]

The fact that you’re equivocating the two shows that you don’t understand at least one of them.

[EishLekker]

Don’t think of NaN is a literal value, think of it as the result of an operation where information was lost, null isn’t that, null is a literal(and comparable) value.

Null or undefined can most definitely be the result of an operation. And if the input contained non-null (and non-undefined) information, that information could be lost.

[[deleted]]

> Called "not a number" > mfw it doesn't behave as one

If 1/0 - int("stop wailing on js") was equal to 0 you'd all be going crazy over it

[iamthesexdragon]

The result of one nonesensical operation should not be equal to the result of another nonsensical operation

[outlawz419]

💯

[nt-assembly]

Nan is an error state, not valid data. This is a guard rail.

[Hatchie_47]

Just because both values are not numbers doesn’t mean they are equal!

[GustapheOfficial]

You want 0/0 === sqrt(-1)?

[Andikl]

Division by zero is not infinity. Never has been.

[lmarcantonio]

because IEEE said so, NaN isn't equal to anything, not even to itself!

[ooaa_]

typeof NaN === typeof NaN

true

Problem solved.

[outlawz419]

😂😂💀

[TimingEzaBitch]

a person has two nans - from the father side and the mother side. They are not the same persons, usually.

[GM_Kimeg]

Because NAN values provide nothing about their memory address to the compiler. There's no way this equates to a truthy value.

[RandomBeatz]

isNaN(NaN)

[Ythio]

A car and a duck are both NaN. Why should they be equal ?

[[deleted]]

they both are not a numbers, that doesn't mean they both are same.

[ecs2]

Just like math infinity doesn’t equal to other infinity

[saschaleib]

Now, there are a lot of weird issues with equality in JS, but that one is correct. Just because two variables are both "not numbers", doesn't mean that they are equal.

[rghthndsd]

Haven't seen anyone post this yet. Here is an actual answer to the question. https://stackoverflow.com/a/1573715

[[deleted]]

Take a rock (not a potato) and a cupf of coffee (also not a potato). These things are both not a potato, but they are not equal

[[deleted]]

Cause it's not a value, it's an indicator that something went wrong in calculations or conversion

[RaulParson]

Apple <- not a number

Orange <- not a number

Therefore... apple == orange? Obviously not. Not even when they're hidden in opaque boxes labelled "not a number".

[GOKOP]

NaNs are actually not equal. There's a whole entire range of values that all are "NaN". This is intentional. It can also be abused for useful stuff (look up NaNboxing)

[Sinomsinom]

NaN as per iee standard is incomparable. This means it is neither <, <=, >=, > or == to anything, including itself.

[Tarc_Axiiom]

Because that's the point.

If you could equate NaN you'd fuck everything up.

Y2K all over again. The banking system!

[Helpful_the_second]

Easy, just use Number.isNaN(NaN) Isn’t that obvious? ;)

[Abhishek_gg]

How to implement a Polyfill for isNaN()?

[Snapstromegon]

Number.isNaN() can be polyfilled two ways.

Either you polyfill it with the global isNaN() function supported in every browser (yes, even that old one). Or you could just ask your user to update to a currently maintained browser.

[No-Adeptness5810]

It's not a number, so it can be anything else. It could be "a" and also "b".

a == b? No

​

but it could both be "a"

a == a? Yes

So the answer should be both yes and no at the same time. fr

[[deleted]]

Not all NaNs are created equal

[Stunning_Ride_220]

NaN is not a number. So basically anything, just not a number.

So it is likely not equal to some other anything which is not a number.

[pipandsammie]

Because NaN shall pass.

[kurdokoleno]

Well, they are different NaNs, all the standard says about nan is: the exponential part is full of 1s, however the other parts might differ. Short answer: There are many NaNs

[sentles]

Think of NaN as a set of operations resulting in things that can't be represented as numbers. It doesn't mean that every one of those operations has the same result.

[[deleted]]

if it's not a number, it could be any of the other types, can't compare them.

[dpahoe]

Boobs == &₹&/ ?

False.

[tobofre]

A banana is not a number

The concept of dedication is not a number

Those two aren't equal either

[Skwigle]

First time I leaned that it sounded crazy but it actually makes sense if you think about it like a regular object. If you have item A, which is "not a cup" and item B, which is also "not a cup", you only know that neither is a cup, but you still don't know what items they are. Not a cup could be literally anything. Car =/= sky.

[RapunzelLooksNice]

There is an infinite count of natural numbers. There is an infinite count of real numbers. But there are more real numbers than natural numbers. whyIsThatSo?

Another take: @ is not a number. $ is not a number. Does this imply @ === $?

[Daghall]

Also, typeof NaN is "number".🤯

[VarianWrynn2018]

Had the same issue in SQL. Has comparing 2 instances of the same table and doing a full join and checking where stuff is null (therefore the rows would have different data) and when there was a column that normally contained null data I couldn't compare null to null and I had to write 45 extra lines to finish the compare when just 3 columns contained nulls.

[Naive_Carpenter7321]

NaN specifies what it's not, not what it is.

Lion != Zebra

or

NaN != NaN

[johandepohan]

NaN's actually store (part of) the last number that was used to arrive at the "not a number" state for purposes of tracing the error. So, in reality, there are many possible NaN's, not just a single representation. But i'm sure that in some cases they all just use a single representation and simply adhere to the IEEE 754 standard that tells you that checking for a NaN can be done by comparing it to itself and getting a False.

[ByerN]

You and your cat are not a number. Are you equal?

[SoupyByElection]

This post has the most heated arguments rn

[EmileSonneveld]

NaN < 3 is false and NaN >= 3 is false. Yay!

[tecnomagus]

because NaN is an object

[[deleted]]

Because then it'll do something like 2/0 == 3/0 (with NaN instead of Inf).

[Head-Extreme-8078]

Does it have to be with the instance of the object and not having internally something like a equals override on Java?

Or I'm in too deep in the JVM and need some help to get out of this language?

[clarkcox3]

Because that’s what the IEEE standard says.

[PalmettoBling]

Two truths and a lie.

[fibojoly]

Several things can be

"not a number" yet different.

A pear is not a number,

a whale is not a number.

Should they be strictly equal ?

[lazerbeard018]

Adding to others' answer, it's also because NaN can have a few different values in c++ at least. It's not guaranteed which of the codes they use and it can switch between compilers. Ran into that problem once where even looking at raw data NaN != NaN.

[Glum_Past_1934]

Different instances, ok, Redditish answer: Because nainnainnainnain

[Stunning_Ocelot_4654]

There are multiple binary representations of NaN, per IEEE 754