Join two records into single record in xslt - xslt-2.0

Question

Request
<Records>
<Record>
<ACCOUNT>460029</ACCOUNT>
<ENTITY>1851</ENTITY>
<UD1>FY17</UD1>
<UD2>457001</UD2>
<UD3>116029</UD3>
<UD4>0</UD4>
<UD5>458004</UD5>
<UD6>Dec</UD6>
<UD7>DeferredIncome</UD7>
<AMOUNT>0</AMOUNT>
</Record>
<Record>
<ACCOUNT>460029</ACCOUNT>
<ENTITY>1851</ENTITY>
<UD1>FY17</UD1>
<UD2>457001</UD2>
<UD3>116029</UD3>
<UD4>0</UD4>
<UD5>458004</UD5>
<UD6>Dec</UD6>
<UD7>OutsBalance</UD7>
<AMOUNT>3400</AMOUNT>
</Record>
<Record>
<ACCOUNT>460029</ACCOUNT>
<ENTITY>1851</ENTITY>
<UD1>FY17</UD1>
<UD2>457002</UD2>
<UD3>116029</UD3>
<UD4>0</UD4>
<UD5>458008</UD5>
<UD6>Jan</UD6>
<UD7>DeferredIncome</UD7>
<AMOUNT>20</AMOUNT>
</Record>
<Record>
<ACCOUNT>460029</ACCOUNT>
<ENTITY>1851</ENTITY>
<UD1>FY17</UD1>
<UD2>457002</UD2>
<UD3>116029</UD3>
<UD4>0</UD4>
<UD5>458008</UD5>
<UD6>Jan</UD6>
<UD7>OtsBalance</UD7>
<AMOUNT>0</AMOUNT>
</Record>
</Records>
response
<Records>
<Record>
<ACCOUNT>460029</ACCOUNT>
<ENTITY>1851</ENTITY>
<UD1>FY17</UD1>
<UD2>457001</UD2>
<UD3>116029</UD3>
<UD4>0</UD4>
<UD5>458004</UD5>
<UD6>Dec</UD6>
<DeferredIncome>0</DeferredIncome>
<OutsBalance>3400</OutsBalance>
</Record>
<Record>
<ACCOUNT>460029</ACCOUNT>
<ENTITY>1851</ENTITY>
<UD1>FY17</UD1>
<UD2>457002</UD2>
<UD3>116029</UD3>
<UD4>0</UD4>
<UD5>458008</UD5>
<UD6>Jan</UD6>
<DeferredIncome>20</DeferredIncome>
<OutsBalance>0</OutsBalance>
</Record>
</Records>
<br/>
I have a requirement where i need to merge two records into one records in xslt.There will be more than 1000 records so running for-each inside for-each will increase number of iteration.
Is there any better way of doing it?Any help is appreciated.Basically each unique record(from Amount to UD7) will have two records deffredAmount and outsBalance. Need to club these two records with defferedAmount and outsBalance

Answer 1

As I already suggested in a comment, this seems to be like a text book case to use the new XSLT 3 feature for-each-group group-by composite="yes", i.e. to use a sequence of items you want to use as the grouping keys for the group-by expression and to indicate with composite="yes" that all of them form the composite key to group items.
So for your example with the XSLT 3 code
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
exclude-result-prefixes="#all"
expand-text="yes"
version="3.0">
<xsl:mode on-no-match="shallow-copy"/>
<xsl:output method="xml" indent="yes"/>
<xsl:template match="Records">
<xsl:copy>
<xsl:for-each-group select="Record" group-by="*[position() le 8]" composite="yes">
<xsl:copy>
<xsl:apply-templates select="* except (UD7, AMOUNT)"/>
<DeferredIncome>{ sum(current-group()[UD7 = 'DeferredIncome']/AMOUNT) }</DeferredIncome>
<OutsBalance>{ sum(current-group()[UD7 = ('OtsBalance', 'OutsBalance')]/AMOUNT) }</OutsBalance>
</xsl:copy>
</xsl:for-each-group>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
which at https://xsltfiddle.liberty-development.net/bdxtqC outputs
<?xml version="1.0" encoding="UTF-8"?>
<Records>
<Record>
<ACCOUNT>460029</ACCOUNT>
<ENTITY>1851</ENTITY>
<UD1>FY17</UD1>
<UD2>457001</UD2>
<UD3>116029</UD3>
<UD4>0</UD4>
<UD5>458004</UD5>
<UD6>Dec</UD6>
<DeferredIncome>0</DeferredIncome>
<OutsBalance>3400</OutsBalance>
</Record>
<Record>
<ACCOUNT>460029</ACCOUNT>
<ENTITY>1851</ENTITY>
<UD1>FY17</UD1>
<UD2>457002</UD2>
<UD3>116029</UD3>
<UD4>0</UD4>
<UD5>458008</UD5>
<UD6>Jan</UD6>
<DeferredIncome>20</DeferredIncome>
<OutsBalance>0</OutsBalance>
</Record>
</Records>
I am not sure whether the check UD7 = ('OtsBalance', 'OutsBalance') was necessary due to typos in your sample data or whether your real data needs that because it contains different spellings of that element value.