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POHow to count the number of concurrent users using time interval data?
 

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    <p>I have a data set representing data from a log file which shows users and machine taking a connection for a server. I have a connection start time (variable start) and end time (variable end) in the dataset:</p> <pre><code>tdata &lt;- structure(list(username = structure(c(9L, 6L, 7L, 5L, 3L, 2L, 4L, 8L, 1L, 4L), .Label = c("ESSAA", "HBRTE", "HPAIUS", "KOLA", "MAITAEN", "MARKEA", "MIAINN", "MSALA", "PAREDT"), class = "factor"), machine = structure(c(3L, 2L, 4L, 8L, 1L, 5L, 9L, 6L, 7L, 9L), .Label = c("D5785.domain.com", "D5874.domain.com", "D5927.domain.com", "D6000.domain.com", "D6092.domain.com", "D6147.domain.com", "D6142.domain.com", "D6169.domain.com", "D6194.domain.com"), class = "factor"), start = structure(c(1322672567, 1322687984, 1322465646, 1322696883, 1322695042, 1322697073, 1322697547, 1322692794, 1322697694, 1322700934), tzone = "", class = c("POSIXct", "POSIXt")), end = structure(c(1322693766, 1322695797, 1322696945, 1322697004, 1322697284, 1322697303, 1322697781, 1322700307, 1322700667, 1322701224), tzone = "", class = c("POSIXct", "POSIXt"))), .Names = c("username", "machine", "start", "end"), row.names = c(NA, 10L), class = "data.frame") &gt; tdata username machine start end 1 PAREDT D5927.domain.com 2011-11-30 19:02:47 2011-12-01 00:56:06 2 MARKEA D5874.domain.com 2011-11-30 23:19:44 2011-12-01 01:29:57 3 MIAINN D6000.domain.com 2011-11-28 09:34:06 2011-12-01 01:49:05 4 MAITAEN D6169.domain.com 2011-12-01 01:48:03 2011-12-01 01:50:04 5 HPAIUS D5785.domain.com 2011-12-01 01:17:22 2011-12-01 01:54:44 6 HBRTE D6092.domain.com 2011-12-01 01:51:13 2011-12-01 01:55:03 7 KOLA D6194.domain.com 2011-12-01 01:59:07 2011-12-01 02:03:01 8 MSALA D6147.domain.com 2011-12-01 00:39:54 2011-12-01 02:45:07 9 ESSAA D6142.domain.com 2011-12-01 02:01:34 2011-12-01 02:51:07 10 KOLA D6194.domain.com 2011-12-01 02:55:34 2011-12-01 03:00:24 &gt; </code></pre> <p>Now I would like to calculate <strong>the number of concurrent users</strong> for each minute using start and end times from the <code>tdata</code> dataset. I got this far:</p> <pre><code>#create dataset containing each minute from tdata start.min &lt;- min(tdata$start, na.rm=T) end.max &lt;- max(tdata$end, na.rm=T) tinterval &lt;- seq.POSIXt(start.min, end.max, by = "mins") </code></pre> <p>Any ideas how to proceed with the calculation?</p>
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