lass="r-msg co"><span class="r-pr">#&gt;</span> gf_line() uses </span>
<span class="r-msg co"><span class="r-pr">#&gt;</span>     * a formula with shape y ~ x. </span>
<span class="r-msg co"><span class="r-pr">#&gt;</span>     * geom:  line </span>
<span class="r-msg co"><span class="r-pr">#&gt;</span>     * key attributes:  alpha, color, fill, group, linetype, linewidth, lineend,</span>
<span class="r-msg co"><span class="r-pr">#&gt;</span>                    linejoin, linemitre, arrow</span>
<span class="