xsl:preceding - only display first value

with a column having repeating values such as:

.
.0045
.0045
.0045
.0046
.0044
.0046
.0045
.0045
.0045
.0045


I would like to display on the first value if there are repeats, so it would appear as:

.
.0045
blank
blank
.0046
.0044
.0046
.0045
blank
blank
blank


   <xsl:if test="not(following-sibling::Step[ProbDefault = current()/ProbDefault]) or not(preceding-sibling::Step[ProbDefault = current()/ProbDefault])">
		<xsl:value-of select="ProbDefault"/>
	   </xsl:if>	 


this code is close, but does not work completely, it creates:

.
.0045
blank
blank
.0046
.0044
.0046
blank
blank
blank
.0045


the problem is that the last .0045 ought to be blank and be moved up three places.

any idea how to do this?

Thanks,
Dmitri