[R] Sum every n (4) observations by group

[Miluji Sb]

Dear Peter,

Thanks so much for your reply and the code! This is helpful.

What I would like is the data.frame below - sum values for *4140, 4141,
4142, 4143 *and then for *4144, 4145, 4146, 4147 *for IDs A, B, and C. Does
that make sense? Thanks again!

Best.

Milu

results <- structure(list(ID = c("A", "A", "A", "A", "A", "A", "A", "A",
"B", "B", "B", "B", "B", "B", "B", "B", "C", "C", "C", "C", "C",
"C", "C", "C"), Date = c(4140L, 4141L, 4142L, 4143L, 4144L, 4145L,
4146L, 4147L, 4140L, 4141L, 4142L, 4143L, 4144L, 4145L, 4146L,
4147L, 4140L, 4141L, 4142L, 4143L, 4144L, 4145L, 4146L, 4147L
), Value = c(0.000207232, 0.000240141, 0.000271414, 0.000258384,
0.00024364, 0.00027148, 0.000280585, 0.000289691, 0.000298797,
0.000307903, 0.000317008, 0.000326114, 0.00033522, 0.000344326,
0.000353431, 0.000362537, 0.000371643, 0.000380749, 0.000389854,
0.00039896, 0.000408066, 0.000417172, 0.000426277, 0.000435383
), sum = c(NA, NA, NA, 0.000977171, NA, NA, NA, 0.001054089,
NA, NA, NA, 0.001213399, NA, NA, NA, 0.001395514, NA, NA, NA,
0.001541206, NA, NA, NA, 0.001686898)), class = "data.frame", row.names =
c(NA,
-24L))

On Sun, Dec 19, 2021 at 7:50 PM Peter Langfelder <peter.langfelder using gmail.com>
wrote:

> I'm not sure I understand the task, but if I do, assuming your data
> frame is assigned to a variable named df, I would do something like
>
> sumNs = function(x, n)
> {
>    if (length(x) %%n !=0) stop("Length of 'x' must be a multiple of 'n'.")
>    n1 = length(x)/n
>    ind = rep(1:n1, each = n)
>    tapply(x, ind, sum)
> }
> sums = tapply(df$Value, df$ID, sumNs, 4)
>
> Peter
>
> On Sun, Dec 19, 2021 at 10:32 AM Miluji Sb <milujisb using gmail.com> wrote:
> >
> > Dear all,
> >
> > I have a dataset (below) by ID and time sequence. I would like to sum
> every
> > four observations by ID.
> >
> > I am confused how to combine the two conditions. Any help will be highly
> > appreciated. Thank you!
> >
> > Best.
> >
> > Milu
> >
> > ## Dataset
> > structure(list(ID = c("A", "A", "A", "A", "A", "A", "A", "A",
> > "B", "B", "B", "B", "B", "B", "B", "B", "C", "C", "C", "C", "C",
> > "C", "C", "C"), Date = c(4140L, 4141L, 4142L, 4143L, 4144L, 4145L,
> > 4146L, 4147L, 4140L, 4141L, 4142L, 4143L, 4144L, 4145L, 4146L,
> > 4147L, 4140L, 4141L, 4142L, 4143L, 4144L, 4145L, 4146L, 4147L
> > ), Value = c(0.000207232, 0.000240141, 0.000271414, 0.000258384,
> > 0.00024364, 0.00027148, 0.000280585, 0.000289691, 0.000298797,
> > 0.000307903, 0.000317008, 0.000326114, 0.00033522, 0.000344326,
> > 0.000353431, 0.000362537, 0.000371643, 0.000380749, 0.000389854,
> > 0.00039896, 0.000408066, 0.000417172, 0.000426277, 0.000435383
> > )), class = "data.frame", row.names = c(NA, -24L))
> >
> >         [[alternative HTML version deleted]]
> >
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