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))) 

Answer 2

Perhaps you are looking for something like this:

> tail(df, -1) - head(df, -1)    ID Score 2   1    -4 3   1    -4 4   1    -4 5   1    -4 6   1    -4 7   1    -4 8   1    -4 9   1    -4 10  1    -4 

You can subtract or add two data.frames together if they are the same dimensions. So, what we are doing here is subtracting one data.frame that is missing the first row (tail(df, -1)) and one that is missing the last row (head(df, -1)) and subtracting them.