xts assignment changes column class - r

Question

I have a data.frame earlyCloses defined as follows:
earlyCloses <- read.table('EarlyCloses.txt', header=T, colClasses= c(rep("character", 3)))
earlyCloses
StartDate EndDate EarlyClose
1 2012-12-24 2012-12-24 13:00
I define a xts object pricesXts as follows:
prices <- read.table('sample.txt', header=T, colClasses=c("character", "numeric"))
pricesXts = xts(prices$Close, as.POSIXct(prices$Date, tz='America/New_York'))
colnames(pricesXts) = c("Close")
pricesXts$CloseTime = NA
pricesXts
Close CloseTime
2012-12-21 13190.84 NA
2012-12-24 13139.08 NA
2012-12-26 13114.59 NA
2012-12-27 13096.31 NA
2012-12-28 12938.11 NA
Now I execute a for loop over the rows of earlyCloses and set the CloseTime of pricesXts.
for (i in 1:nrow(earlyCloses)) {
pricesXts[paste(earlyCloses[i,"StartDate"], earlyCloses[i,"EndDate"], sep='/'), 2] = earlyCloses[i,"EarlyClose"]
}
pricesXts
Close CloseTime
2012-12-21 "13190.84" NA
2012-12-24 "13139.08" "13:00"
2012-12-26 "13114.59" NA
2012-12-27 "13096.31" NA
2012-12-28 "12938.11" NA
Why has the class of the Close column in the xts object changed from numeric to character? Is this because an xts object is represented internally as a matrix? Is there a way to avoid this conversion?

Answer 1

xts is encoded internally as a matrix ( better performances). Since you want just to store the Early Close, you can convert it to a numeric , for example:
strptime(earlyCloses$EarlyClose,'%H:%M')$hour
Then
for (i in 1:nrow(earlyCloses))
pricesXts[paste(earlyCloses[i,"StartDate"],
earlyCloses[i,"EndDate"],
sep='/'), 2] <- strptime(earlyCloses$EarlyClose,'%H:%M')$hour
Close CloseTime
2012-12-21 13191 NA
2012-12-24 13139 13
2012-12-26 13115 NA
2012-12-27 13096 NA
2012-12-28 12938 NA