On Jan 25, 2011, at 9:58 PM, eric wrote:
I want to use diff to take the differences in a column "Close" of a
data
frame "y". But I'd like to do it using the transform function so a
new data
frame is created with a difference column. The problem is that diff
gives
one less than the number of elements in the original data frame. So
transform gives an error message. I know the first element of diff
should be
NA or ideally 0. But not sure how I get there. Any suggestions ?
j
Date Close
1 11/20/1985 156.412
2 11/21/1985 155.112
3 11/22/1985 154.182
4 11/25/1985 154.192
5 11/26/1985 153.722
6 11/27/1985 153.712
d <-diff(j[,2])
d
[1] -1.30 -0.93 0.01 -0.47 -0.01
j <- transform(j, delta=diff(j[,2]))
> j <- transform(j, delta=c(NA, diff(j[,2])))
> j
Date Close delta
1 11/20/1985 156.412 NA
2 11/21/1985 155.112 -1.30
3 11/22/1985 154.182 -0.93
4 11/25/1985 154.192 0.01
5 11/26/1985 153.722 -0.47
6 11/27/1985 153.712 -0.01
Error in data.frame(list(Date = c(5620L, 5639L, 5657L, 5706L, 5721L,
5736L :
arguments imply differing number of rows: 6, 5
Calls: transform -> transform.data.frame -> do.call -> data.frame
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