[R] Caculate first difference from a dataframe; write a simulation

[Gavin Simpson]

On Tue, 2009-08-04 at 23:42 +0530, Meenu Sahi wrote:
> Dear R Users
> 
> I'm writing my first simulation in R.
> I've put across my problems with a smaller example in the attachment along
> with the questions.

Q1 - mydat4[, 1:2] is not a matrix! It is a data.frame.

> class(mydat4[, 1:2])
[1] "data.frame"
> is.matrix(mydat4[, 1:2])
[1] FALSE

?diff is explicit about 'x' needing to be a numeric vector or a matrix.

Cast mydat4[, 1:2] as a matrix and it will work:

> diff(as.matrix(mydat4[,1:2]),1)
   Level spread
3   0.27   2.27
6   0.15   0.01
8   0.58  -2.15
9   0.48   1.43
81 -0.48  -1.43
91  0.48   1.43
2   0.17   0.26
10  0.95  -2.38
1  -0.83   1.94
11  0.32  -1.36

HTH

G

> 
> Please help.
> 
> Best regards
> Meenu
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