I am having troubles with a data transformation I am trying to do. I have a column of data (Ex. 1,2,3,4,5,6,7,8,9)I want to create a new column that looks back n rows and concatenates the values into a new value, preferably an integer. For example, if the lookback window is 3 in my example, the new column would be Nan, Nan, 123, 234,345,456,567,678,789.