diff - R how can I calculate difference between rows in a data frame

Question

Here is a simple example of my problem:

> df <- data.frame(ID=1:10,Score=4*10:1)
> df
       ID Score
    1   1    40
    2   2    36
    3   3    32
    4   4    28
    5   5    24
    6   6    20
    7   7    16
    8   8    12
    9   9     8
    10 10     4
    > diff(df)

Error in r[i1] - r[-length(r):-(length(r) - lag + 1L)] : 
  non-numeric argument to binary operator

Can anyone tell me why this error occurs?

Answer 1

diff wants a matrix or a vector rather than a data frame. Try

data.frame(diff(as.matrix(df)))