Averaging a sequence in blocks

Problem

You want to chop a sequence of data into blocks of a given length, and find the average of each block. This is one way of smoothing data.

Solution

Suppose you have a numeric vector and want to find the average of the first four numbers, the second four, and so on.

  1. # Generate a vector with 22 random numbers from 0-99
  2. set.seed(123)
  3. x <- floor(runif(22)*100)
  4. x
  5. #>  [1] 28 78 40 88 94  4 52 89 55 45 95 45 67 57 10 89 24  4 32 95 88 69
  7. # Round up the length of vector the to the nearest 4
  8. newlength <- ceiling(length(x)/4)*4
  9. newlength
  10. #> [1] 24
  12. # Pad x with NA's up to the new length
  13. x[newlength] <- NA
  14. x
  15. #>  [1] 28 78 40 88 94  4 52 89 55 45 95 45 67 57 10 89 24  4 32 95 88 69 NA NA
  17. # Convert to a matrix with 4 rows
  18. x <- matrix(x, nrow=4)
  19. x
  20. #>      [,1] [,2] [,3] [,4] [,5] [,6]
  21. #> [1,]   28   94   55   67   24   88
  22. #> [2,]   78    4   45   57    4   69
  23. #> [3,]   40   52   95   10   32   NA
  24. #> [4,]   88   89   45   89   95   NA
  26. # Take the means of the columns, and ignore any NA's
  27. colMeans(x, na.rm=TRUE)
  28. #> [1] 58.50 59.75 60.00 55.75 38.75 78.50