[R] roll weekly data to monthly level [SEC=UNCLASSIFIED]

[Augusto.Sanabria at ga.gov.au]

Julia,

I had a similar query a while ago which I solved using
a suggestion from Gabor, have a look at:

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/69597.html

Hope it helps,

Augusto


--------------------------------------------
Augusto Sanabria. MSc, PhD.
Mathematical Modeller
Risk & Impact Analysis Group
Geospatial & Earth Monitoring Division
Geoscience Australia (www.ga.gov.au)
Cnr. Jerrabomberra Av. & Hindmarsh Dr.
Symonston ACT 2601
Ph. (02) 6249-9155






-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of liujb
Sent: Tuesday, 13 January 2009 8:58
To: r-help at r-project.org
Subject: [R] roll weekly data to monthly level



Dear R users:

I have a data set that looks something like this:
ID    time           y
1    2/01/2008    4
1    2/09/2008    12
1    9/01/2008    8
2    1/06/2008    3
2    3/01/2008    4
2    3/09/2008    9
2    6/03/2008    4
3    1/02/2008    3
3    1/10/2008    8
3    2/02/2008    7
3    2/10/2008    3

I'd like to sum up the weekly data to the monthly level, so that it looks something like this:

ID    time       y
1    2/2008    16
1    9/2008    8
2    1/2008    3
2    3/2008    13
2    6/2008    4
3    1/2008    11
3    2/2008    10


What is the best way to do it?

Time must be character. How do I truncate a character so that I can remove the date and only keep the month and year?

Thank you very much in advance.
Julia
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