Compare XSL values in array - arrays

Question

I'm not sure how to title this post..
I want to compare pubDate between rows
Desired Output: Only print the pubDate when it is different from the previous row's pubDate. (my substring function returns Dec 2014, Jan 2015, etc)
Currently I have it set to print the pubDate every time. I just can't figure out how to compare the value between rows... please help!
Code excerpt:
<xsl:template match="item">
<xsl:variable name="Rows" select="channel/item"/>
<xsl:variable name="RowCount" select="count($Rows)"/>
<xsl:variable name="item_link" select="link"/>
<xsl:variable name="item_title" select="description"/>
<xsl:value-of select="$Rows"/>
<xsl:variable name="CurPosition" select="position()" />
<xsl:variable name="PrevPosition" select="position()-1" />
<xsl:variable name="RssFeedLink" select="$rss_WebPartID" />
<xsl:variable name="CurrentElement" select="concat($RssFeedLink,$CurPosition)" />
<xsl:if test="not(substring(pubDate,3,9) = 0)">
<div align="center">
<hr/>
<xsl:value-of select="substring(pubDate,3,9)" disable-output-escaping="yes"/>
</div>
</xsl:if>
<li>
<a href="{$item_link}" title="{$item_title}">
<xsl:variable name="SafeHtml">
<xsl:call-template name="GetSafeHtml">
<xsl:with-param name="Html" select="title"/>
</xsl:call-template>
</xsl:variable>
<xsl:value-of select="$SafeHtml" disable-output-escaping="yes"/>
</a>
</li>
Here is the full code for anybody who wants it:
<xsl:stylesheet xmlns:x="http://www.w3.org/2001/XMLSchema"
version="1.0" exclude-result-prefixes="xsl ddwrt msxsl rssaggwrt"
xmlns:ddwrt="http://schemas.microsoft.com/WebParts/v2/DataView/runtime"
xmlns:rssaggwrt="http://schemas.microsoft.com/WebParts/v3/rssagg/runtime"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:msxsl="urn:schemas-microsoft-com:xslt"
xmlns:rssFeed="urn:schemas-microsoft-com:sharepoint:RSSAggregatorWebPart">
<xsl:param name="rss_FeedLimit">30</xsl:param>
<xsl:param name="rss_ExpandFeed">true</xsl:param>
<xsl:param name="rss_LCID">1033</xsl:param>
<xsl:param name="rss_WebPartID">RSS_Viewer_WebPart</xsl:param>
<xsl:param name="rss_alignValue">left</xsl:param>
<xsl:param name="rss_IsDesignMode">True</xsl:param>
<xsl:output method="xml" omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:variable name="Rows" select="channel/item"/>
<xsl:variable name="RowCount" select="count($Rows)"/>
<div>
<xsl:apply-templates select="rss/channel"/>
</div>
</xsl:template>
<xsl:template match="rss/channel">
<xsl:variable name="link" select="link"/>
<xsl:variable name="description" select="description"/>
<ul>
<xsl:apply-templates select="item"/>
</ul>
</xsl:template>
<xsl:template match="item">
<xsl:variable name="Rows" select="channel/item"/>
<xsl:variable name="RowCount" select="count($Rows)"/>
<xsl:variable name="item_link" select="link"/>
<xsl:variable name="item_title" select="description"/>
<xsl:value-of select="$Rows"/>
<xsl:variable name="CurPosition" select="position()" />
<xsl:variable name="RssFeedLink" select="$rss_WebPartID" />
<xsl:variable name="CurrentElement" select="concat($RssFeedLink,$CurPosition)" />
<xsl:if test="not(substring(pubDate,3,9) = 0)">
<div align="center">
<hr/>
<xsl:value-of select="substring(pubDate,3,9)" disable-output-escaping="yes"/>
</div>
</xsl:if>
<li>
<a href="{$item_link}" title="{$item_title}">
<xsl:variable name="SafeHtml">
<xsl:call-template name="GetSafeHtml">
<xsl:with-param name="Html" select="title"/>
</xsl:call-template>
</xsl:variable>
<xsl:value-of select="$SafeHtml" disable-output-escaping="yes"/>
</a>
</li>
</xsl:template>
<xsl:template name="GetSafeHtml">
<xsl:param name="Html"/>
<xsl:choose>
<xsl:when test="$rss_IsDesignMode = 'True'">
<xsl:value-of select="$Html"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="rssaggwrt:MakeSafe($Html)"/>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>

Answer 1

If you want to check the value of previous "row" you can use the preceding-sibling axis operator.
So, instead of writing this....
<xsl:if test="not(substring(pubDate,3,9) = 0)">
Write this...
<xsl:if test="not(substring(pubDate,3,9) = 0) and not(pubDate = preceding-sibling::item[1]/pubDate)">
Note the use of the [1] here. Doing preceding-sibling will return all nodes preceding the current one, and you only want the first one.
Also note, you might be tempted to write this...
<xsl:if test="not(substring(pubDate,3,9) = 0) and pubDate != preceding-sibling::item[1]/pubDate">
But this will not work for the first item element, because for that expression to be true the preceding sibling would have to exist.
Finally, this will only really work if the item elements are in pub-date order. A better approach would be to consider this a grouping problem, and group the items by date. For XSLT 1.0 you would use a technique called Muenchian Grouping.