How can I check if a node value is a number using XPath?
Any ideas?
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7 Answers
Test the value against NaN:
<xsl:if test="string(number(myNode)) != 'NaN'">
<!-- myNode is a number -->
</xsl:if>
This is a shorter version (thanks @Alejandro):
<xsl:if test="number(myNode) = myNode">
<!-- myNode is a number -->
</xsl:if>
2 Comments
Lucero
The short version by @Alejandro completely fails with XPath 2.0 due to type mismatch on the = operator (
Required item type of first operand of '=' is numeric; supplied value has item type xs:string;), Dimitre's solution works fine however.The shortest possible way to test if the value contained in a variable $v can be used as a number is:
number($v) = number($v)
You only need to substitute the $v above with the expression whose value you want to test.
Explanation:
number($v) = number($v) is obviously true, if $v is a number, or a string that represents a number.
It is true also for a boolean value, because a number(true()) is 1 and number(false) is 0.
Whenever $v cannot be used as a number, then number($v) is NaN
and NaN is not equal to any other value, even to itself.
Thus, the above expression is true only for $v whose value can be used as a number, and false otherwise.
answered Oct 4, 2010 at 17:09
Dimitre Novatchev
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9 Comments
LarsH
+1 helpful explanation. Can someone comment on cases where
number($v) = number($v) yields a different result from number($v) = $v?Dimitre Novatchev
@LarsH: I already commented on these cases. Can you point out yet an undiscussed case?
LarsH
I meant could someone list the cases where
number($v) = number($v) yields a different result from number($v) = $v? Doubtless that's derivable from what you wrote, but I'm not seeing where you addressed this question explicitly. Sorry if I'm being dense. IOW, does your solution and @Oded's/@Alejandro's solution always yield the same results?Dimitre Novatchev
@EricS, It seems one can only access the IEEE standard by purchasing it... Byt do have a look here: cs.berkeley.edu/~wkahan/ieee754status/IEEE754.PDF . In particular, this paragraph: "IEEE 754 assigns values to all relational expressions involving NaN . In the syntax of C , the predicate x != y is True but all others, x < y , x <= y , x == y , x >= y and x > y , are False whenever x or y or both are NaN"
Vayth
14 years later, I faced this issue and your solution helped! This is one of the case where
number($v) = $v fails me because the $v (or in my case is a tag instead of a variable) is defined as numeric on its schema. That's why when testing the expression, I got element is invalid - The value 'N/A' is invalid according to its datatype. This is where NaN is not equal to any other value, even to itself helps. |
There's an amazing type test operator in XPath 2.0 you can use:
<xsl:if test="$number castable as xs:double">
<!-- implementation -->
</xsl:if>
Comments
I'm not trying to provide a yet another alternative solution, but a "meta view" to this problem.
Answers already provided by Oded and Dimitre Novatchev are correct but what people really might mean with phrase "value is a number" is, how would I say it, open to interpretation.
In a way it all comes to this bizarre sounding question: "how do you want to express your numeric values?"
XPath function number() processes numbers that have
- possible leading or trailing whitespace
- preceding sign character only on negative values
- dot as an decimal separator (optional for integers)
- all other characters from range [0-9]
Note that this doesn't include expressions for numerical values that
- are expressed in exponential form (e.g. 12.3E45)
- may contain sign character for positive values
- have a distinction between positive and negative zero
- include value for positive or negative infinity
These are not just made up criteria. An element with content that is according to schema a valid xs:float value might contain any of the above mentioned characteristics. Yet number() would return value NaN.
So answer to your question "How i can check with XPath if a node value is number?" is either "Use already mentioned solutions using number()" or "with a single XPath 1.0 expression, you can't". Think about the possible number formats you might encounter, and if needed, write some kind of logic for validation/number parsing. Within XSLT processing, this can be done with few suitable extra templates, for example.
PS. If you only care about non-zero numbers, the shortest test is
<xsl:if test="number(myNode)">
<!-- myNode is a non-zero number -->
</xsl:if>
1 Comment
LarsH
+1 Good detailed explanation of the issues behind the question: what the OP might have meant or would have meant if he'd known what to ask.
The one I found very useful is the following:
<xsl:choose>
<xsl:when test="not(number(myNode))">
<!-- myNode is a not a number or empty(NaN) or zero -->
</xsl:when>
<xsl:otherwise>
<!-- myNode is a number (!= zero) -->
</xsl:otherwise>
</xsl:choose>
Comments
You could always use something like this:
string(//Sesscode) castable as xs:decimal
castable is documented by W3C here.
Comments
I've been dealing with 01 - which is a numeric.
string(number($v)) != string($v) makes the segregation
