ervations of a period are mapped
to a single time point. This function will convert a datetime variable to
a character vector that reflects the period, instead of a single time point.
<code>strftime</code> is used to format the start and the end of the interval.</p>
    
    </div>

    <pre class="usage"><span class='fu'>format_interval</span>(<span class='no'>x</span>, <span class='kw'>start_format</span> <span class='kw'>=</span> <span class='st'>"%Y-%m-%d"</span>, <span class='kw'>end_format</span> <spa