fnSetColumnVis deletes data ?

function toggleIt() {
	var indices = [];
	$("#myTable tbody tr").first().children("td.myclass").each(function(){
		indices.push($(this).index());
	});
	alert("indices:" + indices);
	for(var ind in indices)
	{
		var iCol = indices[ind];
		var bVis = oTable.fnSettings().aoColumns[iCol].bVisible;
		oTable.fnSetColumnVis( iCol, bVis ? false : true );
	}
}

When I run toggleIt(), I get

"indices: 4,6,7"

inside alert dialog box. Then 4,6 and 7th columns are hidden.
When I run toggleIt() again I get an empty indices array.

When I check DOM, I see that 4,6 and 7th columns are deleted.
Does "fnSetColumnVis" deletes the columns? Is it possible to just hide rather than delete the data?