Filter data from XSLT - xslt

Question

I have a XSL file in which I am creating a field like this:
<ServiceText>
<xsl:value-of select="concat(Yrs,'-',Mos,'-',Days,'-',Hrs)" />
</ServiceText>
The values of 'Yrs,'-',Mos,'-',Days,'-',Hrs , I am receiving from a Web service response and assiging it to the XSL directly. I cannot do any modification to the data in code for these fields, because that is how the ocde is. All data manipulation is on the xslt.
I want to do a data filtering on xslt as follows:
if value of yrs =-1 then yrs=""
if value of mos =-1 then mos=""
if value of Days =-1 then Days=""
if value of Hrs =-1 then Hrs=""
How can I do it on the XSL file?

Answer 1

XSLT 2.0:
<xsl:template match="/root">
<ServiceText>
<xsl:value-of select="string-join((Yrs, Mos, Days, Hrs)[.!=-1],'-')" />
</ServiceText>
</xsl:template>
See link for a Working example

Answer 2

In XSLT 1.0 use something like this:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text"/>
<xsl:strip-space elements="*"/>
<xsl:template match="*/*[not(.= -1)]">
<xsl:value-of select="concat(., substring('-', 2 - not(self::Hrs)))"/>
</xsl:template>
<xsl:template match="*/*[. = -1]"/>
</xsl:stylesheet>
When this transformation is applied on the following XML document:
<t>
<Yrs>-1</Yrs>
<Mos>7</Mos>
<Days>15</Days>
<Hrs>3</Hrs>
</t>
the wanted result is produced:
7-15-3
Do Note:
It seems that there is an assumption that the "-1" values form a contiguous group (right to left in the sequence Yrs, Mos,Days).
If this assumption is violated, it would be impossible to understand what is the missing part in 2013-10-8 -- is it the months or the days ?