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.

# Generate a vector with 23 random numbers from 0-99
set.seed(123)
x <- floor(runif(22)*100)
# 28 78 40 88 94  4 52 89 55 45 95 45 67 57 10 89 24  4 32 95 88 69

# Round up the length of vector the to the nearest 4
newlength <- ceiling(length(x)/4)*4
# 24

# Pad x with NA's up to the new length
x[newlength] <- NA
# 28 78 40 88 94  4 52 89 55 45 95 45 67 57 10 89 24  4 32 95 88 69 NA NA

# Convert to a matrix with 4 rows
x <- matrix(x, nrow=4)
#      [,1] [,2] [,3] [,4] [,5] [,6]
# [1,]   28   94   55   67   24   88
# [2,]   78    4   45   57    4   69
# [3,]   40   52   95   10   32   NA
# [4,]   88   89   45   89   95   NA

# Take the means of the columns, and ignore any NA's
colMeans(x, na.rm=TRUE)
# 58.50 59.75 60.00 55.75 38.75 78.50