Say you have a dataset, where each row has a date or time, and something is recorded for that date and time. If each row is a unique date – great! If not, you may have rows with the same date, and you have to combine records for the same date to get a daily tally.

Here is how you can make a daily tally (or a monthly or yearly one; the frequency of tallies is not important):

1. convert the dates to numbers. R will say 01/01/1970 is day 1, 02/01/1970 is day 2, …, 07/03/2010 is day 14675; 31/12/1960 is day -1.
2. use a “for loop” to lump entries from the same date together
3. calculate the daily by calculating the number of rows in the daily lump (I do this below), or by adding all entries in a particular column in a daily lump

To get the daily total,

summary(rott[,2])<-as.numeric(as.Date(rott[,2], format=”%m/%d/%Y”, origin = “3/7/2010″))

daily<-matrix(NA,184,1)

for(i in 1:184) #my data spans 184 days from 7th March to 6th Sept 2010
{
rott.i<-rott[rott[,2]==14674+i,]   daily[i,1]<-nrow(rott.i) #7th March 2010 is the 14675th day from 01/01/1970, the day the R calendar starts
}

acf(daily,main=”Autocorrelation of Timeseries”) #ACF!

Abbas Keshvani