On Nov 16, 2010, at 2:33 PM, Paolo Rossi wrote:
Hi,
Can anyone suggest a clever way to compute a rolling weekly average
of the
columns in a matrix? The column bit is straightforward use apply
given a
function which does what you want on a column. With regard to a
particular
column, the obvious way is to run a for loop indexing the last 7
days and
computing the average . I simply would like to know if there is a
better /
quicker way.
There is a rollmean function in package zoo. See below.
Code:
Given a,
a= array(1:100, dim = c(17,2))
a
[,1] [,2]
[1,] 1 18
[2,] 2 19
[3,] 3 20
[4,] 4 21
[5,] 5 22
[6,] 6 23
[7,] 7 24
[8,] 8 25
[9,] 9 26
[10,] 10 27
[11,] 11 28
[12,] 12 29
[13,] 13 30
[14,] 14 31
[15,] 15 32
[16,] 16 33
[17,] 17 34
one needs to start computing the average from obs 7 s (at obs 7 you
have a
full week to compute the average) and compute the rolling weekly
average
from day 7 onwards
Results will look like b
[,1] [,2]
[1,] 4 14
[2,] 5 21
I think you got your first ones out of sequence:
> apply(a, 2, rollmean, k=7)
[,1] [,2]
[1,] 4 21
[2,] 5 22
[3,] 6 23
[4,] 7 24
[5,] 8 25
[6,] 9 26
[7,] 10 27
[8,] 11 28
[9,] 12 29
[10,] 13 30
[11,] 14 31
--
David.
[3,] 6 22
[4,] 7 23
[5,] 8 24
[6,] 9 25
[7,] 10 26
[8,] 11 27
[9,] 12 28
[10,] 13 29
Thanks in advance,
Paolo
On 15 November 2010 20:59, wangwallace <talentt...@gmail.com> wrote:
Hey,
I am hoping someone can help me with a sampling question.
I have a data frame of 8 variables (the first column is the
subjects' id):
SubID CSE1 CSE2 CSE3 CSE4 WSE1 WSE2 WSE3 WSE4
1 6 5 6 2 6 2
2 4
2 6 4 7 2 6 6
2 3
3 5 5 5 5 5 5
4 5
4 5 4 3 4 4 4
5 2
5 5 6 7 5 6 4
4 1
6 5 4 3 6 4 3
7 3
7 3 6 6 3 6 5
2 1
8 3 6 6 3 6 5
4 7
the 6 variables are categorized into two groups with CSE1, CSE2,
CSE3, and
CSE4 in one group and the rest in another group.
sample(data[,2:4],2,replace=FALSE)
CSE1 CSE2
1 6 5
2 6 4
3 5 5
4 5 4
5 5 6
6 5 4
7 3 6
8 3 6
Now I want to sample 1 column from another group of variables
(i.e., WSE1,
WSE2, WSE3, WSE4), but I want to restrict a vector I am going to
sample
from
to only those columns that are not correspond to GROUP 1 variables
I have
sampled. That is, I want to sample a column from WSE3, WSE4 Columns
corresponding to CSE1 and CSE2 (i.e., WSE1, WSE2) need to be dropped.
How can I do this? what if I want to repeat this whole process
(drawing 2
random columns from CSE1, CSE2, CSE3, and CSE4 first, AND then
another
random column from WSE1, WSE2, WSE3, and WSE4) for 1000 times. any
ideas?
Many thanks in advance!!
--
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David Winsemius, MD
West Hartford, CT
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