Is there an if -then - else statement in XPath

Question

It seems with all the rich amount of function in xpath that you could do an  if    However   my engine keeps insisting  there is no such function    and I hardly find any documentation on the web  I found some dubious sources   but the syntax they had didn t work    I need to remove     from the end of a string  if exist   so I wanted to do this   if  fn ends-with   div   id  head   text                      then  fn substring-before   div   id  head   text                       else    div   id  head   text      Any advice

User · Answer

The official language specification for XPath 2.0 on W3.org details that the language does indeed support if statements. See Section 3.8 Conditional Expressions, in particular. Along with the syntax format and explanation, it gives the following example:

if ($widget1/unit-cost < $widget2/unit-cost) 
  then $widget1
  else $widget2

This would suggest that you shouldn't have brackets surrounding your expressions (otherwise the syntax looks correct). I'm not wholly confident, but it's surely worth a try. So you'll want to change your query to look like this:

if (fn:ends-with(//div [@id='head']/text(),': '))
  then fn:substring-before(//div [@id='head']/text(),': ')
  else //div [@id='head']/text()

I do strongly suspect this may fix it however, as the fact that your XPath engine seems to be trying to interpret if as a function, where it is in fact a special construct of the language.

Finally, to point out the obvious, insure that your XPath engine does in fact support XPath 2.0 (as opposed to an earlier version)! I don't believe conditional expressions are part of previous versions of XPath.

User · Answer

Yes  there is a way to do it in XPath 1 0    concat    substring  s1  1  number  condition         string-length  s1      substring  s2  1  number not  condition     string-length  s2       This relies on the concatenation of two mutually exclusive strings  the first one being empty if the condition is false  0   string-length        the second one being empty if the condition is true  This is called  Becker s method   attributed to Oliver Becker   In your case    concat    substring      substring-before   div  id  head   text               1       number        ends-with   div  id  head   text                      string-length substring-before   div   id  head   text                  substring        div  id  head   text         1       number not        ends-with   div  id  head   text                       string-length   div  id  head   text            Though I would try to get rid of all the      before   Also  there is the possibility that   div  id  head   returns more than one node  Just be aware of that  mdash  using   div  id  head   1  is more defensive

User · Answer

Somewhat simpler XPath 1 0 solution  adapted from Tomalek s  posted here  and Dimitre s  here    concat substring  s1  1 div number  cond    substring  s2  1 div number not  cond       Note  I found an explicit number   was required to convert the bool to an int otherwise some XPath evaluators threw a type mismatch error  Depending on how strict your XPath processor is type-matching you may not need it

User · Answer

Unfortunately the previous answers were no option for me so i researched for a while and found this solution   http   blog alessio marchetti name post 2011 02 12 the-Oliver-Becker-s-XPath-method  I use it to output text if a certain Node exists  4 is the length of the text foo  So i guess a more elegant solution would be the use of a variable   substring  foo  number not normalize-space  elements the element     4

User · Answer

according to pkarat s  law you can achieve conditional XPath in version 1 0   For your case  follow the concept   concat substring-before your-xpath contains              your-xpath not contains             This will definitely work  See how it works  Give two inputs  praba  karan   For 1st input  it contains   so condition true  string before    will be the output  say praba is your output  2nd condition will be false so no problems   For 2nd input  it does not contain   so condition fails  coming to 2nd condition the string doesn t contain   so condition true    therefore output karan will be thrown   Finally your output would be praba karan

User · Answer

How about using fn replace string pattern replace  instead   XPATH is very often used in XSLTs and if you are in that situation and does not have XPATH 2 0 you could use      lt xsl choose gt       lt xsl when test  condition1  gt        condition1-statements      lt  xsl when gt       lt xsl when test  condition2  gt        condition2-statements      lt  xsl when gt       lt xsl otherwise gt        otherwise-statements      lt  xsl otherwise gt     lt  xsl choose gt

User · Answer

Personally  I would use XSLT to transform the XML and remove the trailing colons   For example  suppose I have this input    lt  xml version  1 0  encoding  UTF-8   gt   lt Document gt       lt Paragraph gt This paragraph ends in a period  lt  Paragraph gt       lt Paragraph gt This one ends in a colon  lt  Paragraph gt       lt Paragraph gt This one has a   in the middle  lt  Paragraph gt   lt  Document gt    If I wanted to strip out trailing colons in my paragraphs  I would use this XSLT    lt  xml version  1 0  encoding  UTF-8   gt   lt xsl stylesheet      xmlns xsl  http   www w3 org 1999 XSL Transform       xmlns fn  http   www w3 org 2005 xpath-functions      version  2 0  gt       lt  -- identity -- gt       lt xsl template match       node    gt           lt xsl copy gt               lt xsl apply-templates select     node     gt           lt  xsl copy gt       lt  xsl template gt       lt  -- strip out colons at the end of paragraphs -- gt       lt xsl template match  Paragraph  gt           lt xsl choose gt               lt  -- if it ends with a   -- gt               lt xsl when test  fn ends-with         gt                   lt xsl copy gt                       lt  -- copy everything but the last character -- gt                       lt xsl value-of select  substring    1  string-length   -1   gt  lt  xsl value-of gt                   lt  xsl copy gt               lt  xsl when gt               lt xsl otherwise gt                   lt xsl copy gt                       lt xsl apply-templates  gt                   lt  xsl copy gt               lt  xsl otherwise gt           lt  xsl choose gt       lt  xsl template gt   lt  xsl stylesheet gt

[xpath] Is there an "if -then - else " statement in XPath?

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