  ECSTDTC <span class='op'>=</span> <span class='fu'><a href='https://rdrr.io/r/base/c.html'>c</a></span><span class='op'>(</span><span class='st'>"2021-01-01"</span>, <span class='st'>"2021-02-01"</span>, <span class='st'>"2021-03-01"</span>, <span class='st'>"2021-04-01"</span>, <span class='st'>"2021-05-01"</span>, 
                             <span class='st'>"2021-01-01"</span>, <span class='st'>"2021-02-01"</span>, <span class='st'>"2021-03-01"</span>, <span class='st'>"2021-04-01"</span>, <span clas