lists vs. NumPy arrays for sets of dates and strings

[beliavsky at aol.com]

I am going to read a multivariate time series from a CSV file that looks like

Date,A,B
2014-01-01,10.0,20.0
2014-01-02,10.1,19.9
...

The numerical data I will store in a NumPy array, since they are more convenient to work with than lists of lists. What are the advantages and disadvantages of storing the symbols [A,B] and dates [2014-01-01,2014-01-02] as lists vs. NumPy arrays?