New matrix containing difference between row elements of original

Question

I want to take an existing MxN matrix and create a new M-1xN matrix such that for each columns, the elements are the difference between adjacent row elements of the original

Answer 1

It's very simple for numerical data (not sure why you have characters):

diff(m)

With the character data, this should work:

diff(matrix(as.numeric(m), dim(m)))

Answer 2

In case you want to subtract the columns of a matrix (and not the rows), try:

col.diff = t(diff(t(mat)))

Answer 3

It's a bit strange with the character format, but here's a way:

# Set up the data
mymat<-matrix(c("17","16","15",
  "34","32","32",
  "53","47","48" ,
  "72","62","63",
  "90","78","79" ,
  "109","94","96"),nrow=6,byrow=TRUE)

Use the apply function with an anonymous function centered around diff.

apply(mymat, 2, function(x)as.character(diff(as.numeric(x))))

#      [,1] [,2] [,3]
# [1,] "17" "16" "17"
# [2,] "19" "15" "16"
# [3,] "19" "15" "15"
# [4,] "18" "16" "16"
# [5,] "19" "16" "17"

If the data are numeric to begin with and a numeric result is desired, then the above could be simplified to

apply(mymat, 2, diff)