The most D3 way to do this would be to chain the selectors using the filter
method:
var list1 = d3.selectAll(".mYc").filter(".101");
This won't work though because class names cannot start with a number. So you have to rename to something like "a101" and then you can do
var list1 = d3.selectAll(".mYc").filter(".a101");
See this fiddle.