¿Cómo contar el número de usuarios simultáneos que usan datos de intervalo de tiempo?

Question

Tengo un conjunto de datos que representa datos de un archivo de registro que muestra a los usuarios y la máquina tomando una conexión para un servidor. Tengo una hora de inicio de conexión (salida variable) y de final (extremo variable) en el conjunto de datos:

tdata <- 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") 

> 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 
> 

Ahora me gustaría para calcular el número de usuarios simultáneos por cada minuto usando tiempos de inicio y fin de el conjunto de datos tdata. Llegué hasta aquí:

#create dataset containing each minute from tdata 
start.min <- min(tdata$start, na.rm=T) 
end.max <- max(tdata$end, na.rm=T) 
tinterval <- seq.POSIXt(start.min, end.max, by = "mins") 

¿Alguna idea de cómo proceder con el cálculo?

Answer 1

Aquí es un ejemplo

n <- sapply(tinterval, function(tt) sum(tdata$start <= tt & tt <= tdata$end)) 

continuación

@> tail(data.frame(tinterval, n)) 
       tinterval n 
3922 2011-12-01 09:55:06 0 
3923 2011-12-01 09:56:06 1 
3924 2011-12-01 09:57:06 1 
3925 2011-12-01 09:58:06 1 
3926 2011-12-01 09:59:06 1 
3927 2011-12-01 10:00:06 1 
@> plot(tinterval, n, type = "l") 

bastante lento, aunque ...

Answer 2

Sólo por diversión, aquí es una solución XTS:

library(xts) 
# create an empty xts object with the minute timestamps we're interested in 
out <- xts(,align.time(tinterval,60)) 
# loop over each user 
for(i in 1:NROW(tdata)) { 
    # paste the start/end times into an xts-style range 
    timeRange <- paste(format(tdata[i,c("start","end")]),collapse="/") 
    # add the minute "by parameter" for timeBasedSeq 
    timeRange <- paste(timeRange,"M",sep="/") 
    # create the by-minute sequence and align to minutes to match "out" 
    timeSeq <- align.time(timeBasedSeq(timeRange),60) 
    # create xts object with "1" entries for times between start and end 
    temp <- xts(rep(1,length(timeSeq)),timeSeq) 
    # merge temp with out and fill non-matching timestamps with "0" 
    out <- merge(out, temp, fill=0) 
} 
# add column names (if necessary) 
colnames(out) <- tdata[,1] 
# sum across rows (need xts constructor because rowSums returns a matrix) 
counts <- xts(rowSums(out),index(out))