[R] Selecting ranges of dates from a dataframe

[David Winsemius]

On Mar 10, 2011, at 8:23 AM, Benjamin Stier wrote:

> Hello list!
>
> I have a data.frame which looks like this:
>> serv
> datum op.read op.write   read   write
> 1   2011-01-29 10:00:00       0        0      0       0
> 2   2011-01-29 10:00:01       0        0      0       0
> 3   2011-01-29 10:00:02       0        0      0       0
> 4   2011-01-29 10:00:03       0        4      0  647168
> 5   2011-01-29 10:00:04       0        0      0       0
> 6   2011-01-29 10:00:05       0       14      0 1960837
> 7   2011-01-29 10:00:06       0        0      0       0
> ...
> 115 2011-01-30 10:00:54       0        0      0       0
> 116 2011-01-30 10:00:55       0        0      0       0
> 117 2011-01-30 10:00:56       0        0      0       0
> 118 2011-01-30 10:00:57      54        0  29184       0
> 119 2011-01-30 10:00:58     204        0 122880       0
> 120 2011-01-30 10:00:59       0        0      0       0
> ...
>
> I want to compare read/write from each day. I already have a  
> solution, but it
> is pretty slow.

See if this is any faster:
 > aggregate(serv[, c("read", "write")], list(format(serv$datum, "%Y- 
%m-%d")), sum)
      Group.1    read    write
1 2011-01-29 1021439 11726356
2 2011-01-30 1089534  4634910

>
> # read the data
> serv <- read.delim("cut.inp")
>
> # Reformat the dates from the file
> serv$datum <- strptime(serv$datum,  "%Y-%m-%d %H:%M:%S")
>
> # select all single days
> dates.serv <- unique(strptime(serv$datum, format="%Y-%m-%d"))
>
> # create a data.frame
> values <- data.frame(row.names=1, datum=numeric(0),  
> write=numeric(0), read=numeric(0))
> for(i in as.character(dates.serv)) {
>        # build up a values for a day-range
>        searchstart <- as.POSIXlt(paste(i, "00:00:00", sep=" "))
>        searchend <- as.POSIXlt(paste(i, "23:59:59", sep=" "))
>        # select all values from a specific day
>        day <- serv[(serv$datum >= searchstart & serv$datum <=  
> searchend),]
>        write <- as.numeric(sum(as.numeric(day$write)))
>        read <- as.numeric(sum(as.numeric(day$read)))
>        # add to the data.frame
>        values <- rbind(values, data.frame(datum=i, write=write,  
> read=read))
> }
>
> This is my first try using R for statistics so I'm sure this isn't  
> the best
> solution.
> The for-loop does it's job, but as I said is really slow. My data is  
> for 21
> days and 1 line per second.
> Is there a better way to select the date-ranges instead of a for- 
> loop? The
> line where I select all values for "day" seems to be the heaviest.  
> Any idea?
>
> Kind regards,
>
> Benjamin
>
> PS: I attached some sample data, in case you want to try for yourself.
> <cut.inp>______________________________________________
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David Winsemius, MD
West Hartford, CT