Late to the party, but in the spirit of TIMTOWTDI, here is a non-nested map solution:

perl   -anE '$d ||={map {$_=>$x++} @wd=qw[Mon Tue Wen Thu Fri Sat Sun]
+};
     $F[1] and  $v{$F[1]}->[$d->{$F[0]}] = "X"
    }{
    say map{"\t$_"}@wd;
    say "$_\t",map {"$_\t"}@{$v{$_}} for sort keys %v'    ts-data.txt
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