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isnum() vs. NaN

bochmann
Path Finder

Has anyone run into the interesting effect that isnum() thinks that "NaN" is a number?

So

isnum("NaN") is true
"NaN" * 2 = "NaN"

but

tonumber("NaN") is NULL

Are there any other odd, uh, numbers besides Not a Number?

I made up the following silly query as an illustration:

 

 

 

| makeresults
| eval num="blubb;NaN;100;0.5;0,5;-0;NULL;"
| makemv delim=";" allowempty=true num 
| mvexpand num
| eval isnum=if(isnum(num),"true","false")
| eval isint=if(isint(num),"true","false")
| eval isnull=if(isnull(num),"true","false")
| eval calcnum=num*2
| eval isnumcalcnum=if(isnum(calcnum),"true","false")
| eval isnullcalcnum=if(isnull(calcnum),"true","false")
| eval numnum=tonumber(num)
| eval isnumnum=if(isnum(numnum),"true","false")
| eval isnullnumnum=if(isnull(numnum),"true","false")
| table num,isnum,isint,isnull,calcnum,isnumcalcnum,isnullcalcnum,numnum,isnumnum,isnullnumnum

 

 

 

 

 which results in

num isnum isint isnull calcnum isnumcalcnum isnullcalcnum numnum isnumnum isnullnumnum
                   
blubb false false false   false true   false true
NaN true false false NaN true false   false true
100 true true false 200 true false 100 true false
0.5 true false false 1 true false 0.5 true false
0,5 false false false   false true   false true
-0 true true false -0 true false -0 true false
NULL false false false   false true   false true
  false false false   false true   false true


(Post moved over from the Splunk Enterprise group.)

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bochmann
Path Finder

So, I've been talking to Splunk support, which directed me to the documentation at SearchReference/Eval  that kind of mentions that NaN is special, and also pointed to typeof() as alternative.

Initially, this seemed like a good idea, but unfortunately typeof() is even more interesting:

| makeresults
| eval t=typeof("NaN")
| eval num="NaN"
| eval tnum=typeof(num)

...returns

t = String
tnum = Number

Oh well....?

 

0 Karma

yuanliu
SplunkTrust
SplunkTrust

Support is correct that documented behavior is not a bug.  That explains your original observation about tonumber.

Your observation about typeof is also normal.  Imagine you are the interpreter.  In typeof("NaN"), you are given a string literal.  Of course you say that's of type String.  In typeof(num), you are given a variable whose value is documented as a number.  You say that's of type Number.

0 Karma

bochmann
Path Finder

Well, Splunk doesn't treat inf and -inf, mentioned in that same section, as a number either.

Anyways, I need to add additional logic to sanitize inputs that might have fields with the text "NaN" (does occasionally happen when the source is a SQL query) either way - for most purposes it just isn't a number, and tends to cause problems in further processing.

0 Karma

yuanliu
SplunkTrust
SplunkTrust
the text "NaN" (does occasionally happen when the source is a SQL query) either 

This explains it.  I was wondering why typeof(num) should be Number when num had value "NaN". Whoever wrote that code in typeof must have SQL in mind.  A SQL query only returns "NaN" when the data type is numeric.  If you are programming against results from a SQL query in any language, you always need to write a logic for this possible return.

0 Karma

richgalloway
SplunkTrust
SplunkTrust

Smells like a bug to me.  Consider reporting it to Splunk Support and/or https://ideas.splunk.com

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