Hey R professionals,

I have a large dataset and I want to run a loop on it basically creating a
new column which gathers information from another reference table.

When I run the code, R just freezes and even does not response after 30min
which is really unusual. I tried sapply as well but does not improve at
all.

I am running R 3.0.2 on Windows 7.  I checked the system, when I run the
code, my CPU usage is about 25%-30% that is taxing my desktop.

Here is my code:

#df1 is the data set I want to add a new column#
#b is the reference tabel#

for (i in (1:nrow(df1))) {
  begin=which(b$Time2==df1$start[i] & b$Date==df1$Date[i])
  date=unlist(strsplit(as.character(dff$end[i])," "))[1]
   end=ifelse(date=="2013-10-17",
   which(b$Time2==df1$end[i] & b$Date==df1$Date[i]),
   which(b$Time2==df1$end[i]-3600*24 & b$Date==as.Date(df1$Date[i])+1))
    df1$new[i] <- sum(b[begin:end,]$Power)
}

And here is a mimic sample of df1 & b:

df1 <- structure(list(Date = structure(c(1369699200, 1369699200,
1369699200,
1369699200, 1369699200), tzone = "UTC", class = c("POSIXct",
"POSIXt")), start = structure(c(1381991205, 1381990247, 1382010454,
1382007281, 1381992288), tzone = "UTC", class = c("POSIXct",
"POSIXt")), end = structure(c(1381992405, 1381993727, 1382010694,
1382007461, 1381992468), tzone = "UTC", class = c("POSIXct",
"POSIXt"))), .Names = c("Date", "start", "end"), row.names = c(NA,
-5L), class = "data.frame")


b <- structure(list(Date = structure(c(1369699200, 1369699200, 1369699200,
1369699200, 1369699200, 1369699200, 1369699200, 1369699200, 1369699200,
1369699200, 1369699200, 1369699200, 1369699200, 1369699200, 1369699200,
1369699200, 1369699200, 1369699200, 1369699200, 1369699200, 1369699200,
1369699200, 1369699200, 1369699200, 1369699200, 1369699200, 1369699200,
1369699200, 1369699200, 1369699200, 1369699200, 1369699200, 1369699200,
1369699200, 1369699200, 1369699200, 1369699200, 1369699200, 1369699200,
1369699200, 1369699200, 1369699200, 1369699200, 1369699200, 1369699200,
1369699200, 1369699200, 1369699200, 1369699200, 1369699200), tzone = "UTC",
class = c("POSIXct",
"POSIXt")), Time2 = structure(c(1381989634, 1381989694, 1381989754,
1381989814, 1381989874, 1381989934, 1381989994, 1381990054, 1381990114,
1381990174, 1381990234, 1381990294, 1381990354, 1381990414, 1381990474,
1381990534, 1381990594, 1381990654, 1381990714, 1381990774, 1381990834,
1381990894, 1381990954, 1381991014, 1381991074, 1381991134, 1381991194,
1381991254, 1381991314, 1381991374, 1381991434, 1381991494, 1381991554,
1381991614, 1381991674, 1381991734, 1381991794, 1381991854, 1381991914,
1381991974, 1381992034, 1381992094, 1381992154, 1381992214, 1381992274,
1381992334, 1381992394, 1381992454, 1381992514, 1381992574), tzone = "UTC",
class = c("POSIXct",
"POSIXt")), Power = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,
45, 46, 47, 48, 49, 50)), .Names = c("Date", "Time2", "Power"
), row.names = c(NA, -50L), class = "data.frame")

Thanks for your help!

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