[R] Help on manipulating a data frame

[Alfonso Sammassimo]

Hi R-experts,



I have a large set of weekly data in this format:



2007-01-05 -1.52377151
2007-01-12  1.04787390
2007-01-19  0.61647047
2007-01-26  1.87864283
2007-02-02  0.54992405
2007-02-09  1.96850069
2007-02-16  0.26850159
2007-02-23  1.56305144
2007-03-02 -4.19500573
2007-03-09  0.77127814
2007-03-16  0.32387312
2007-03-23  2.02163219
2007-03-30  0.63175605
2007-04-06  1.33346284
2007-04-13  0.96021569



How might this data be sorted to something like this?:



Date               Week of Month     Value

2007-01-05          1                     -1.52377151
2007-01-12          2                      1.04787390
2007-01-19          3                      0.61647047
2007-01-26          4                      1.87864283

2007-02-02          1                      0.54992405



My aim is to return the last value of every month where the previous values 
in that month were negative values, hence the need to split the data by 
month. Any guide as to how this might this be possible without a loop?



Any help would be much appreciated.



Thanks,



Alf Sammassimo

Melbourne, Australia