Creating a for loop to subset data on R - r

Question

I have a huge set of data that in the .csv format has 2 columns (one Date_time and other is Q.vanda).
This is what the head and tail of the data looks like,
> head(mdf.vanda)
Date_Time Q.vanda
1 1969-12-05 21:00:00 0
2 1969-12-05 21:01:00 4
3 1969-12-05 21:05:00 11
4 1969-12-05 21:20:00 17
5 1969-12-05 22:45:00 27
6 1969-12-05 22:55:00 23
> tail(mdf.vanda)
Date_Time Q.vanda
165738 2016-01-19 10:15:00 2995.25
165739 2016-01-19 10:30:00 2858.04
165740 2016-01-19 10:45:00 2956.94
165741 2016-01-19 11:00:00 2972.52
165742 2016-01-19 11:15:00 2776.99
165743 2016-01-19 11:30:00 3082.53
There are 48 years of data in between and I want to create a for loop to subset them by year (ex. from 1969/10/01 to 1970/10/01, 1970/10/01 to 1971/10/01 etc.)
I wrote a code but, it's giving me an error that I am not able to resolve. I am pretty new at R so, feel free to suggest some other code that you might think is more efficient for my purpose.
code:
cut <- as.POSIXct(strptime(as.character(c('1969/10/01','1970/10/01','1971/10/01','1972/10/01','1973/10/01','1974/10/01','1975/10/01','1976/10/01','1977/10/01','1978/10/01','1979/10/01','1980/10/01','1981/10/01','1982/10/01','1983/10/01','1984/10/01','1985/10/01','1986/10/01','1987/10/01','1988/10/01','1989/10/01','1990/10/01','1991/10/01','1992/10/01','1993/10/01','1994/10/01','1995/10/01','1996/10/01','1997/10/01','1998/10/01',
'1999/10/01','2000/10/01','2001/10/01','2002/10/01','2003/10/01','2004/10/01',
'2005/10/01','2006/10/01','2007/10/01','2008/10/01','2009/10/01','2010/10/01',
'2011/10/01','2012/10/01','2013/10/01','2014/10/01','2015/10/01','2016/10/01')),format = "%Y/%m/%d"))
df.sub <- as.data.frame(matrix(data=NA,nrow=14496, ncol=96)) #nrow = (31+30+31+31+28)*(4*24)[days * readings/day] , ncol = (48*2)[Seasons*cols]
i.odd <- seq(1,49, by=2)
for (i in 1:48) {df.sub[1:length(mdf.vanda$Date_Time[mdf.vanda$Date_Time >= cut[i] & mdf.vanda$Date_Time < cut[i+1]])
,i.odd[i]:(i.odd[i]+1)] <- subset(mdf.vanda,mdf.vanda$Date_Time > cut[i] & mdf.vanda$Date_Time < cut[i+1])}
Error:
Error in [<-.data.frame(*tmp*, 1:length(mdf.vanda$Date_Time[mdf.vanda$Date_Time >= :
replacement element 1 has 1595 rows, need 1596

Answer 1

you can split your data as shown
split(mdf.vanda,findInterval(as.Date(mdf.vanda$Date_Time),seq(as.Date("1969-10-01"),as.Date("2016-10-01"),"1 year"))

Answer 2

There is no need for a loop here. Base R has the cut function to perform this very operation and significantly faster than the loop. Since you have the break points defined with your "cut" variable.
#cut <- as.POSIXct(c('1969/10/01', ... ,'2016/10/01'),format = "%Y/%m/%d")
mytime<-cut(mdf.vanda$Date_Time, breaks = cut, include.lowest = TRUE)
The variable "mytime" is a vector the length of your data frame with a label to bin the data.
You could then use the split function to break your dataframe in a list of data frames or use the group_by function from the dplyr library for additional data processing.

Answer 3

I suggest you have a look at the convenient quantmod package. Once you have Time Series data, you can use the apply.yearly function and apply any function to every year of data.