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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...

...request: BadValue (integer parameter out of range for operation) Major opcode of failed request: 128 (Apple-DRI) Minor opcode of failed request: 2 () Value in failed request: 0x1000004 Serial number of failed request: 365 Current serial number in output stream: 365 [2011-07-03 00:00:23Z #0] [ID:0] ERROR: ResourceManager - RDBSource_c::ProcessRequest. Resource 1010513:3664656 does not exist in any available RDB sources. [2011-07-03 00:00:23Z #0] [ID:0] ERROR: ResourceManager - RDBSource_c::ProcessRequest. Resource 1010214:3664656 does not exist in any available RDB sources. Anyo...