Plotting the autocorrelation function

The autocorrelation function, is very important if you want to find the interrelationship between time series using the lagged values. The acf function will plot the correlation between all pairs of data points with lagged values. The plot will have two horizontal blue dashed lines at -0.2 and 0.2, representing the upper and lower bounds. If auto-correlation coefficients are close to zero, this means that there is no relationship, so time series are also known as white noise.

Getting ready

You have already completed the previous recipes and familiar with time series.

How to do it...

Perform the following steps with R:

> sales = sample(400:10000, 72, replace= TRUE) 
> sales 
Output: 
 
 [1] 3304 7697 6715 3906 8963 9240 1423 5330 8298 7747 1686 2917 2004 4591 2213 1977 
[17] 1101 7624 2814 4002 8284 6016 5875 6936 1336 6090 4190 7437 1968 3070 4013 5186 
[33] 6560 7981 5496 8818 1991 3531 4624  895 5720 8481  826  435 6940 1723 9797 8261 
[49] 8811 4933...