How to make conditional statements of attributes with templates in XSLT

[Milkncookiez]

How can I get the value of an attribute and use it in a conditional statement. For example I have <O Option="a" LineNr="1"> and this is element is a child under another parent element that gets grouped with other elements. So the condition I want is: if [value-of Option is null] then [do nothing] else-if [check if the value of the attribute of the element under the next parent element with the same value is empty]. And if there are for example 3 parent elements that contain this element with the Option attribute and if all of the attributes are NOT empty - then group them. I have the grouping done, but it is not connected with this attribute that I want to use now. So I need just the formulation of the conditional statements.

edit: giving input and output desired examples

Input example 1:

<Area><Type>A</Type><Street><Position>5</Position><House><L Option="" LineNr="1">--> some elements</L></House></Street><Street><Position>5</Position><Block><O Option="" LineNr="1">--> some elements</O></Block></Street><Street><Position>6</Position><House><L Option="o" LineNr="1">--> some elements</L></House></Street><Street><Position>6</Position><Block><O Option="" LineNr="1">--> some elements</O></Block></Street></Area>

And desired output:

<Area><Type>A</Type><Street><Position>5</Position><House><L Option="" LineNr="1">--> some elements</L></House><Block><O Option="" LineNr="1">--> some elements</O></Block></Street><Street><Position>6</Position><House><L Option="o" LineNr="1">--> some elements</L></House><Block><O Option="" LineNr="1">--> some elements</O></Block></Street></Area>

But if in the same position number, all the occurrences have a value in the Option attribute of L or O, then I want them arranged under the other occurrence of a position number. Like that:

Input example 2:

<Area><Type>A</Type><Street><Position>5</Position><House><L Option="" LineNr="1">--> some elements</L></House></Street><Street><Position>5</Position><Block><O Option="" LineNr="1">--> some elements</O></Block></Street><Street><Position>6</Position><House><L Option="o" LineNr="1">--> some elements</L></House></Street><Street><Position>6</Position><Block><O Option="a" LineNr="1">--> some elements</O></Block></Street></Area>

Then the output will be:

<Area><Type>A</Type><Street><Position>5</Position><House><L Option="" LineNr="1">--> some elements</L></House><Block><O Option="" LineNr="1">--> some elements</O></Block><House><L Option="o" LineNr="1">--> some elements</L></House><Block><O Option="a" LineNr="1">--> some elements</O></Block></Street></Area>

as now position 6 is gone and its child elements are grouped under the upper occurrence position (which is 5 in this case in the same Type) as all of the attributes Option in the L or O elements had value (which can be either "a" or "o", if that is relevant).

And this is the XSLT which I am using now. It only groups the elements of the different occurrences of the same position numbers under one number:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"><xsl:strip-space elements="*" /><xsl:output method="xml" indent="yes" /><xsl:key name="streetByPosition" match="Street" use="concat(../Type, '|', Position)" /><xsl:template match="@*|node()"><xsl:copy><xsl:apply-templates select="@*|node()" /></xsl:copy></xsl:template><!-- for the first Street in each Position --><xsl:template match="Street[generate-id() =generate-id(key('streetByPosition', concat(../Type, '|', Position))[1])]"><Street><!-- copy in the Position element once only --><xsl:apply-templates select="Position" /><!-- copy in all sub-elements except Position from all matching Streets--><xsl:apply-templates select="key('streetByPosition', concat(../Type, '|', Position))/*[not(self::Position)]" /></Street></xsl:template><!-- ignore all other Street elements --><xsl:template match="Street" /></xsl:stylesheet>

I really, really need solution for that and I have no clue how to do it, especially the checks.