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):

- 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.
- use a “for loop” to lump entries from the same date together
- 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!