time       item price
2009-01-01 X    0.65473572
2009-01-01 Y    2.4520609
2009-01-01 Z    -1.46570942
2009-01-02 X    -0.89248112
2009-01-02 Y    0.2154713
2009-01-02 Z    -2.05357735
2009-01-03 X    0.98012375
2009-01-03 Y    1.3179287
2009-01-03 Z    4.64248357
2009-01-04 X    0.35397376
2009-01-04 Y    3.3765645
2009-01-04 Z    -0.25237774
2009-01-05 X    2.19357813
2009-01-05 Y    1.3477511
2009-01-05 Z    0.09719105