d_case</span>(<span class='no'>strings</span>)</div><div class='output co'>#&gt; [1] "this_Is_a_Strange_string" "And_This_Another_One"    
#&gt; [3] NA                        </div><div class='input'><span class='fu'>to_swap_case</span>(<span class='no'>strings</span>)</div><div class='output co'>#&gt; [1] "THIS iS A sTRANGE_STRING" "and this another_oNE"    
#&gt; [3] NA                        </div><div class='input'><span class='fu'>to_sentence_case</span>(<span class='no'>strings</span>)</div><div class