span>(M.front$Ml.perp[[<span class="dv">1</span>]] , M.back$Mr.perp[[last]])

combined &lt;-<span class="st"> </span><span class="kw">data.frame</span>(<span class="dt">angle=</span>angle, <span class="dt">parallel=</span>intensity.par,
                       <span class="dt">perpendicular=</span>intensity.perp,
                       <span class="dt">side =</span> <span class="kw">gl</span>(<span class="dv">2</span>, <span class="kw">length</span>(back$angle),
                                <span class="d