Float numbers comparison

[Chavdar Ivanov]

Dear all,

I have a very basic question...

I need to compare literals that are floats and tried to use two ways. 1) using sh:equals to compare 2 properties and 2) using SPARQL where I filter != different values

For the filter I tried using 

FILTER (xsd:float(?value1)!=xsd:float(?value1)).

or

FILTER (?value1!=?value1).

Both give the same outcome.

Below I listed a summary of the tests I did

I think sh:equals treats the literals as strings even though they are floats. It also gives 2 results. I thing this looks like according to the SHACL spec although I didn't if the sh:equals ignores the datatype. 

However In some cases the result form the SPARQL is kind of strange. It looks like the precision is 10-6, but for the big numbers  and when scientific form on float number is used we have something different. 

What is followed to define the difference?

If I use google calculator

100123456.1-100.123459E+06=-2.90000000596

Normally it should be OK to compare different forms of float.

1) using sh:equals in the property shape

Value1 ; value 2  ; comparisson result

1.123456 ; 1.123456 ; same

1.1234560 ; 1.1234561 ; different (sh:equals reports it twice)

31.1234560 ; 31.1234561 ;different (sh:equals reports it twice)

30    ;      30.0000001 ; different (sh:equals reports it twice)

30     ;      30.000001 ; different (sh:equals reports it twice)

100123456.0  ; 100123456.1 ; different (sh:equals reports it twice)

100123456.0  ; 100123456.0 ; same

100123456    ;  100.123456E6 ; different (sh:equals reports it twice)

100123456    ;  100.123456E+06 ; different (sh:equals reports it twice)

-0.123456789  ;  -123.456789E-3 ; different (sh:equals reports it twice)

-0.123456789  ;  -123.456789E-03 ; different (sh:equals reports it twice)

100123456.1    ;  100.123456E+06  ; different (sh:equals reports it twice)

100123456.1     ;   100.123459E+06 ; different (sh:equals reports it twice)

100123456.1     ;  100123459      ; different (sh:equals reports it twice)

100123456.1     ;  100123459.0    ; different (sh:equals reports it twice)

2) using SPARQL (in the property shape)

1.123456 ; 1.123456 ; same

1.1234560 ; 1.1234561 ; different

31.1234560 ; 31.1234561 ;different

30    ;      30.0000001 ; same

30     ;      30.000001 ; different

100123456.0  ; 100123456.1 ; same

100123456.0  ; 100123456.0 ; same

100123456    ;  100.123456E6 ; same

100123456    ;  100.123456E+06 ; same

-0.123456789  ;  -123.456789E-3 ; same

-0.123456789  ;  -123.456789E-03 ; same

100123456.1    ;  100.123456E+06  ; same

100123456.1     ;   100.123459E+06 ; same

100123456.1     ;  100123459      ; same

100123456.1     ;  100123459.0    ; same

Best regards

Chavdar 

[Holger Knublauch]

On 11/08/2020 06:17, Chavdar Ivanov wrote:

Dear all,

I have a very basic question...

I need to compare literals that are floats and tried to use two ways. 1) using sh:equals to compare 2 properties and 2) using SPARQL where I filter != different values

For the filter I tried using 

FILTER (xsd:float(?value1)!=xsd:float(?value1)).

or

FILTER (?value1!=?value1).

Both give the same outcome.

Below I listed a summary of the tests I did

I think sh:equals treats the literals as strings even though they are floats. It also gives 2 results. I thing this looks like according to the SHACL spec although I didn't if the sh:equals ignores the datatype.

sh:equals will compare the RDF nodes, so the datatype will make a big difference and "1"^^xsd:float will be different from "1"^^xsd:string or integer.

In SPARQL you may be better off with xsd:decimal than xsd:float, as xsd:decimal has more precision. But this is more of a SPARQL/ARQ question for which you may get more qualified help elsewhere, e.g. on jena-users.

Holger

Best regards

Chavdar 

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[Chavdar Ivanov]

Dear Holger,

 

Thanks. I will approach the other forum.

Just to clarify – yes all literals were typed literals with datatype float. So sh:equals was comparing float to float 

Did you mean that I should use xsd:decimal in the SPARQL query although in data graph it is coming as float?

Something like this

?var1 which is float in data graph

?var2 which is float in data graph

xsd:decimal(?var1)!=xsd:decimal(?var2)

 

Best regards

Chavdar 

[Holger Knublauch]

Since sh:equals is based on RDF node equality, values such as "1.0"^^xsd:float and "1"^^xsd:float count as distinct. Maybe that's the issue you are running into?

SPARQL does comparison by (mathematical) values, so 1.0 = 1 there.

Holger

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[Chavdar Ivanov]

Dear Holger,

Thanks.

Yes, I think that explains sh:equals effect.

But SPARQL is a mystery to have some that are correctly compared mathematically such as 

1.123456 ; 1.123456 ; same

1.1234560 ; 1.1234561 ; different

and some that are totally wrong such as

100123456.1     ;  100123459      ; same

100123456.1     ;  100123459.0    ; same

100123456.0  ; 100123456.1 ; same

Best regards

Chavdar