[R] How to group data by day

[Mikhail Titov]

It depends what would you like to get at the end. Perhaps you don't
necessary need this type of numbering. For instance, if you'd like to
calculate daily average.

london$id <- as.Date(london$id)

For sum by day you could use, let's say, this

aggregate(words~id,london,FUN=sum)

If you really want what you've asked:

london$one=1
u=unique(london$id)
z=aggregate(one~id,london,FUN=sum)
london$day=rep(seq(along.with=z$one),z$one)

Mikhail


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Michela Ferron
> Sent: Monday, February 14, 2011 11:09 AM
> To: r-help at r-project.org
> Subject: [R] How to group data by day
> 
> Hi everybody,
> 
> I'm a beginner in R and I'm having a hard time grouping my data by day.
> The data are in this format:
> 
> id; words
> 2005-07-07T09:59:56Z; 35
> 2005-07-07T10:01:39Z; 13
> 2005-07-08T10:02:22Z; 1
> 2005-07-09T10:03:16Z; 23
> 2005-07-10T10:04:23Z; 39
> 2005-07-10T10:04:39Z; 15
> 
> I've transformed the date strings in dates with the function:
> london$id <- transform(london$id, as.Date(london$id, format="%Y-%m-
> %d%T%H:%M:%S%Z"))
> and it seems to work.
> 
> Now I would like to add a new "day" variable to group data by day, like
> this:
> 
> id; words; day
> 2005-07-07T09:59:56Z; 35; 1
> 2005-07-07T10:01:39Z; 13; 1
> 2005-07-08T10:02:22Z; 1; 2
> 2005-07-09T10:03:16Z; 23; 3
> 2005-07-10T10:04:23Z; 39; 4
> 2005-07-10T10:04:39Z; 15; 4
> 
> How can I do that?
> 
> Many thanks!
> 
> Michela
> 
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