create new variable from date data - r

Question

Now my data frame is like below
dput(head(t.zoo))
structure(c(85.92, 85.85, 85.83, 85.83, 85.85, 85.87, 1300, 1300,
1299.75, 1299.75, 1299.75, 1300), .Dim = c(6L, 2L), .Dimnames = list(
NULL, c("cl", "es")), index = structure(list(sec = c(0.400000095367432,
0.900000095367432, 1.40000009536743, 1.90000009536743, 2.40000009536743,
2.90000009536743), min = c(30L, 30L, 30L, 30L, 30L, 30L), hour = c(10L,
10L, 10L, 10L, 10L, 10L), mday = c(6L, 6L, 6L, 6L, 6L, 6L), mon = c(5L,
5L, 5L, 5L, 5L, 5L), year = c(112L, 112L, 112L, 112L, 112L, 112L
), wday = c(3L, 3L, 3L, 3L, 3L, 3L), yday = c(157L, 157L, 157L,
157L, 157L, 157L), isdst = c(1L, 1L, 1L, 1L, 1L, 1L)), .Names = c("sec",
"min", "hour", "mday", "mon", "year", "wday", "yday", "isdst"
), class = c("POSIXlt", "POSIXt"), tzone = c("", "EST", "EDT"
)), class = "zoo")
I have two questions, first is I would like to add a variable name for the first column and 2nd is i want to create a categorical variable to help me indicate 2010-06-06 (since there are 3 separate days)
What I should do for the date data?

Answer 1

I'm not familiar with zoo class, so the following code is not nice, but seems working.
yourdata<-as.matrix(yourdata)
justdate <- substr(rownames(yourdata), 1, 10)
justtime <- substr(rownames(yourdata), 11, 19)
row.names(yourdata) <- NULL
yourdata<-as.data.frame(yourdata)
yourdata[,"justdate"]<-justdate
yourdata[,"justtime"]<-justtime
yourdata[yourdata$justdate=="2012-06-06","newvariable"]<-1
> yourdata
cl es justdate justtime newvariable
1 85.92 1300.00 2012-06-06 10:30:00 1
2 85.85 1300.00 2012-06-06 10:30:00 1
3 85.83 1299.75 2012-06-06 10:30:01 1
4 85.83 1299.75 2012-06-06 10:30:01 1
5 85.85 1299.75 2012-06-06 10:30:02 1
6 85.87 1300.00 2012-06-06 10:30:02 1

Answer 2

zoo objects are a little bit different to work with from data.frames.
The "first column" (as you referred to it) is actually not a column, but the index of your object. Try index(t.zoo) and see what it returns. This index really should have unique values; in your case, there are duplicated values, which might affect your calculations.
Conversion to a data.frame can be done like the following. I've added separate "Date" and "Time" variables based on the index from t.zoo.
require(zoo) # Load the `zoo` package if you haven't already done so
t.df = data.frame(Date = format(index(t.zoo), "%Y-%m-%d"),
Time = format(index(t.zoo), "%H:%M:%S"),
data.frame(t.zoo))
t.df
# Date Time cl es
# 1 2012-06-06 10:30:00 85.92 1300.00
# 2 2012-06-06 10:30:00 85.85 1300.00
# 3 2012-06-06 10:30:01 85.83 1299.75
# 4 2012-06-06 10:30:01 85.83 1299.75
# 5 2012-06-06 10:30:02 85.85 1299.75
# 6 2012-06-06 10:30:02 85.87 1300.00
Converting back to a zoo object (keeping the new "Date" and "Time" columns, or any other columns that you have added) can be done like:
zoo(t.df, order.by=index(t.zoo))
Note, however, that this will give you a warning because you don't have unique "order.by" values.