Subject: Re: [xsl] What is the most efficient XPath expression for retrieving the first child element? From: "Dimitre Novatchev dnovatchev@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> Date: Sun, 12 May 2019 17:27:59 -0000 |
> (b) child::Total_Size This is O(N) because all children will be examined -- and more than one Total_Size elements may be selected. So, this expression is wrong. If we want to select the first child element named Total_Size, here is a correct expression: Total_Size[1] The one that in theory should be more efficient than the above, is: *[1] Why is this more efficient? Because there is no need to get the element's name and compare it to "Total_Size". We just select the first child **regardless** of its name, and spend the few saved nanoseconds smiling :) Note also that we can omit the child:: axis altogether, because it is the "default axis" -- as per the W3C XPath 1.0 Spec: https://www.w3.org/TR/1999/REC-xpath-19991116/#path-abbrev. So a few more nanoseconds saved -- this time in reading and parsing. Cheers, Dimitre On Sun, May 12, 2019 at 4:43 AM Costello, Roger L. costello@xxxxxxxxx < xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote: > Hello XSLT experts! > > I want to retrieve the first child element. The children consist of a > <Total_Size> element followed by many <String> elements (perhaps thousands > of <String> elements). > > <COFF_String_Table> > <Total_Size>4443</Total_Size> > <String>.eh_frame</String> > <String>.debug_aranges</String> > <String>.debug_info</String> > ... > </COFF_String_Table> > > Question: What is the most efficient XPath for selecting the first child > element (the <Total_Size> element)? Assume the context node is the > <COFF_String_Table> element. Which of these is the most efficient XPath > expression: > > (a) child::*[1] > (b) child::Total_Size > (c) something else (what?) > > /Roger
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